Aqueous eletrodeposition of magnetic cobalt-samarium alloys

ABSTRACT

Disclosed are methods and compositions for aqueous electrodeposition of rare earth-transitiona metal alloys (e.g., samarium-cobalt alloys). Also disclosed are nanostructured magnetic coatings comprising a magnetic alloy of a rare earth metal (e.g., samarium) and a transition metal (e.g., cobalt). This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 60/851,389,filed Oct. 13, 2006, and U.S. Application No. 60/852,286, filed Oct. 17,2006, which are hereby incorporated herein by reference in theirentireties.

ACKNOWLEDGEMENT

This invention was made with government support under Grant No.DMI-0089095 awarded by the National Science Foundation. The UnitedStates government has certain rights in the invention.

BACKGROUND

Bulk alloys of transition metals-rare earths are important permanentmagnet materials. When using conventional techniques, however, thecurrent high materials and processing costs of Co—Sm permanent magnetshave limited their application to high temperature and corrosiveenvironments where costs are of secondary importance. More specifically,only high cost metallurgical and physical deposition methods arecurrently in use to fabricate Co—Sm permanent magnets consisting of theintermetallics SmCo₅ and Sm₂Co₁₇.

In contrast, compositions and methods disclosed in U.S. Pat. No.6,306,276 established the basis for the successful electrodeposition ofrare earth-transition metal alloys from aqueous media. Suitableoperating and plating bath conditions to obtain magnetic cobalt-samarium(Co-Sm) alloys from aqueous media for high performance nanostructuredpermanent magnets, however, have remained unknown in the art.

As current estimates of the global market for permanent magnets exceed$5 billion, such suitable operating and plating bath conditions toobtain magnetic cobalt-samarium (Co—Sm) alloys can provide substantialsavings in manufacturing costs and considerable lower materials costsfor nanotechnology applications, thereby greatly expanding the globalmarket share of high performance Co—Sm permanent magnets fabricated byelectrodeposition from aqueous media.

SUMMARY

As embodied and broadly described herein, the invention, in one aspect,relates to

Disclosed are compositions for enhancing the aqueous electrodepositionof rare earth-transition metal alloys comprising a water soluble salt ofsamarium, a water soluble salt of cobalt, and a complexant.

Also disclosed are methods for electrodepositing a samarium-cobaltcoating onto a conducting (e.g., metal) substrate, comprising placing anaqueous solution containing a water soluble salt of samarium, a watersoluble salt of cobalt, one or more supporting electrolytes, and acomplexant into a plating bath, placing an anode and the substrate to becoated into the bath and connecting the anode and the substrate to apower supply, with the substrate acting as a cathode, adjusting the pHof the bath to a suitable operating level, and applying a currentthrough the anode and substrate causing the samarium and the cobalt tomigrate to, and adhere to, the substrate.

Also disclosed are samarium-cobalt coatings produced by the disclosedmethods.

Also disclosed are nanostructured magnetic coatings comprising amagnetic alloy of a rare earth metal and a transition metal.

Unless otherwise expressly stated, it is in no way intended that anymethod or aspect set forth herein be construed as requiring that itssteps be performed in a specific order. Accordingly, where a disclosedmethod or system does not specifically state that the steps are to belimited to a specific order, it is no way intended that an order beinferred, in any respect. This holds for any possible non-express basisfor interpretation, including matters of logic with respect toarrangement of steps or operational flow, plain meaning derived fromgrammatical organization or punctuation, or the number or type ofaspects described in the specification.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, which are incorporated in and constitute apart of this specification, illustrate several aspects and together withthe description serve to explain the principles of the invention.

FIG. 1 shows a graph illustrating maximum energy product for permanentmagnetic materials as a function of time.

FIG. 2 shows a phase diagram of the Sm—Co system.

FIG. 3 shows the Co-rich region of the Sm—Co phase diagram.

FIG. 4 shows the hexagonal CaCu₅ structure of SmCo₅ [C. Barrett and T.B. Massalski, Structure of metals, Pergamon Press, Oxford, New York,(1980), p266].

FIG. 5 shows the rhombohedral Th₂Ni₁₇-type structure of Sm₂Co₁₇ [R. C.O'Handley, Modern magnetic materials, John Wiley & Son, Inc., New York,(2000), pp. 496-502].

FIG. 6 shows the pinning mechanism of Sm₂Co₁₇ [P. Campbell, Permanentmagnet materials and their application, Cambridge University Press, NewYork, (1994), pp. 42-43].

FIG. 7 shows saturation magnetization, coercivity and squareness ofCo—Sm films versus atomic percent of Sm [S. A. Bendson and J. H. Judy,IEEE Trans. Magnetics, 9, 627, (1973)].

FIG. 8 shows variation of resistivity, coercivity, and saturationmagnetization with film (33 nm) composition (left) and SUBSTRATEtemperature (right) under a background pressure of 2×10⁻⁷ Torr^(es).

FIG. 10 shows coercivity (left) and remanence ratio (right) as afunction of the Sm content for samples processed at Ar gas pressures▪6×10⁻², 8×10⁻², and ♦1×10⁻¹ Torr and a constant substrate temperature460° C. [V. Neua and S. A. Shaheen, J. Appl. Phys., 86, 7006, (1999)].

FIG. 11 is of graphs showing the effect of current density, withoscillatory stirring, on the co-deposition of rare earth TM alloyed withnickel, iron and cobalt respectively.

FIG. 12 is a graph showing the effect, with stirring, of glycine/cobaltratio on the deposition of the rare earth cobalt mixture.

FIG. 13 is a graph showing the effect, with stirring, of glycine andcobalt concentration on rare earth cobalt mixture deposition.

FIG. 14 is a graph showing the effect, with stirring, of pulse currentduty cycle on rare earth cobalt mixture deposition.

FIG. 15 is of graphs showing the effect of solution pH and currentdensity on the deposition of Nd—Ni, Nd—FE and Nd—Co, respectively.

FIG. 16 is of graph showing the effect of solution stirring on Ce—Nideposits.

FIG. 17 shows an experimental flowchart of a Hull cell study of DC andPC electrodeposition of Co—Sm alloys.

FIG. 18 shows a design of Hull cell and Hull cell panel.

FIG. 19 shows a schematic of pulse current electrodeposition.

FIG. 20 shows a schematic of the setup for the Hull cellelectrodeposition system.

FIG. 21 shows an energy dispersive spectrum of an electrodeposited Co—Smalloy.

FIG. 22 shows Hull cell patterns of PC electrodeposition from bath 1 at60° C. for different applied current of (a) 4.5 A and (b) 7 A.(T_(on)=10 ms, duty cycle γ=0.1 and applied charge=50 C).

FIG. 23 shows Hull cell patterns of PC electrodeposition from bath I at25° C. for applied charge/deposit area of (a) 100 C/15 cm² and (b) 50C/7.5 cm². (T_(on)=10 ms, duty cycle γ=0.1 and an applied current of 4.5A).

FIG. 24 shows Hull cell patterns obtained from bath 1 at (a) 25° C., (b)60° C. and (c) 80° C.

FIG. 25 shows XRD patterns of deposits #3 obtained from bath 1 at 25° C.and (a) 50 mA/cm², metallic region; (b) 100 mA/cm², burnt region; and(c) 500 mA/cm², oxide/hydroxide region.

FIG. 26 shows Sm deposit content obtained from bath 1 at 25, 60 and 80°C. and various CDs.

FIG. 27 shows a setup for solution agitation in the Hull cell.

FIG. 28 shows Hull cell patterns obtained from Bath 1 ar 25° C. (a)without and (b) with agitation; at 60° C. (c) without and (d) withagitation.

FIG. 29 shows Sm deposit content obtained from bath 1 with/out agitationat 25 and 60° C. and various CD.

FIG. 30 shows Hull cell patterns obtained from Bath 2 (1M Sm sulfamatewithout glycine) at (a) 25° C. and (c) 60° C.; from bath 3 (1M Smsulfamate with 0.15M glycine) at (b) 25° C. and (d) 60° C.

FIG. 31 shows Hull cell patterns obtained from Bath 4 (0.05M Co sulfate)at (a) 25° C. and (b) 60° C.; from bath 5 (0.05M Co sulfate, 0.15Mglycine) at (c) 25° C. and (d) 60° C.

FIG. 32 shows Hull cell patterns obtained from bath 6 (1M Sm sulfamate,0.05M Co sulfate), bath 1 (1M Sm sulfamate, 0.05M Co sulfate, 0.15Mglycine) and bath 7 (1M Sm sulfamate, 0.05M Co sulfate, 3M glycine) at(a)-(c) 25° C. and (d)-(t) 60° C.

FIG. 33 shows Sm deposit content obtained from plating baths containingno, 0.15M and 3M glycine at various CD.

FIG. 34 shows XRD patterns of metallic deposits obtained from bath 1(with 0.15M glycine) at (a) 60° C., 650 mA/cm²and (b) 25° C., 50 mA/cm²and from bath 6 (without glycine) at (c) 60° C., 50 mA/cm² and (d) 25°C., 10 mA/cm².

FIG. 35 shows Hull cell patterns obtained from Bath 1 (1M Sm sulfamate,0.05M Co sulfate, 0.15M glycine) at (a) 25° C. and (b) 60° C.; from Bath8 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, 1M NH₄ sulfamate)at (c) 25° C. and (d) 60° C.

FIG. 36 shows Sm deposit content obtained at 25 and 60° C. from Bath 1(1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine) and Bath 8 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine, 1M sulfamate) at various CD.

FIG. 37 shows Hull cell patterns obtained from Bath 1 at 25° C. for (a)DC, (b) γ=0.1, T.=10 ms and (c) γ=0.1, T_(on)=0.05 ms; at 60° C. for (d)DC, (e) γ=0.1, T_(on)=10 ms and (f) γ=0.1, T.=0.05 ms.

FIG. 38 shows Sm deposit content of deposits obtained from Bath 1 at 25and 60° C. for PC electrodeposition of LH=0.05 and 10 ms (γ=0.1) and forDC electrodeposition at various PCD.

FIG. 39 shows Hull cell patterns obtained from Bath 1 at 25° C. forγ=0.1 (a) T_(on)=0.05 ms, (b) T_(on)=0.1 ms, (c) T_(on)=1 ms and (d)T_(on)=10 ms.

FIG. 40 shows Sm deposit content of deposits obtained from Bath 1 at 25°C. and γ=0.1 for T_(on)=0.05, 0.1, 1 and 10 ms at various PCD.

FIG. 41 shows Hull cell patterns obtained from Bath 1 at 25° C. forT_(on)=0.1 ms at (a) γ=0.05, (b) γ=0.075, (c) γ=0.1, (d) γ=0.2, (e)γ=0.3 and (f) γ=0.3 (DC).

FIG. 42 shows Sm deposit content obtained from Bath 1 at 25° C. andT_(on)=0.1 ms for γ=0.05, 0.075, 0.1, 0.2, 0.3 and 1 (DC) at variousPCD.

FIG. 43 shows dependence of deposit Sm content on current density.

FIG. 44 shows dependence of current efficiency on current density.

FIG. 45 shows dependence of deposit Sm content on temperature.

FIG. 46 shows dependence of current efficiency on temperature.

FIG. 47 shows dependence of magnetic saturation on deposit Sm content(no NH₄ sulfamate).

FIG. 48 shows dependence of coercivity on current density.

FIG. 49 shows topography and microstructure of electrodeposited Co—Smalloys at current densities 100 mA/cm² for plating baths of 60° C. (a)with 1M NH₄ sulfamate, and (b) without NH₄ sulfamate.

FIG. 50 shows XRD of electrodeposited Co—Sm alloys at 100 and 500mA/cm². S=brass substrate.

FIG. 51 shows the effect of CD on Sm content and CE of Co—Sm alloys. 1 MSm sulfamate, 0.05 M Co sulfate, 0.15 M.

FIG. 52 shows the effect of CD on deposit composition; pH 6, 1.2 p.mfilm thickness.

FIG. 53 shows structures of IG-RE-Glycine complexes (17): (a)equilibrium of anionic, zwitterionic and cationic species; (b)hetero-dinuclear trisglycine complex; (c) quasi-diglycine complex; (d)quasi-triglycine complex.

FIG. 54 shows structures of Co—V (a) and Co—Fe—V (b) biscitratecomplexes.

FIG. 55 shows proposed mechanism of electrodeposition of binary andternary IG-V alloys.

FIG. 56 shows structure of Co—Mo (W) biscitrate complexes.

FIG. 57 shows a proposed mechanism of electrodeposition of IG-Mo (W)alloys.

FIG. 58 shows composite Co—W/Cr/Co—W/Cr deposit (12, 24): (a) X500, notheat treated (HT); (b) H. T. in air, 916° C., 10 hrs (unetched); (c) H.T. in carburizing atmosphere, 916° C., 10 hrs (unetched); (d) H. T. incarburizing atmosphere, 916° C., 10 hrs (etchant, hot Murakami).S=cobalt strike.

FIG. 59 shows an experimental flowchart of parametric studies of DCelectrodeposition of Co—Sm alloys.

FIG. 60 shows a set up of DC electrodeposition.

FIG. 61 shows a setup of a RDE system.

FIG. 62 shows a schematic diagram of a VSM.

FIG. 63 shows a hysteresis loop of ED Co—Sm alloys.

FIG. 64 shows the effect of current density and solution temperature on(a) samarium deposit content and (b) current efficiency.

FIG. 65 shows the effect of current density and solution temperature onnormalized charges of Sm, Co and H₂ in Co—Sm alloys electrodeposition.

FIG. 66 shows (a) polarization curves at various current densities andsolution temperatures and (b) dependence of Sm content on cathodicpotential in Co—Sm electrodeposition.

FIG. 67 shows XRD patterns of deposits obtained from bath 1 (1M Smsulfamate, 0.051M Co sulfate, 0.15M glycine, pH 6) at 25° C. and variousCDs).

FIG. 68 shows XRD patterns of deposits obtained from bath 1 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at 60° C. and variousCDs.

FIG. 69 shows XRD patterns of deposits obtained from bath 1 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at (a) 2 mA/cm², (b)25 mA/cm² and (c) 50 mA/cm² at various solution temperatures.

FIG. 70 shows SEM of Co—Sm thin films obtained from bath 1 at 25° C. andat (a)-(c) 2 mA/cm², (d)-(f) 25 mA/cm² and (g)-(i) 50 mA/cm².

FIG. 71 shows SEM of Co—Sm thin films obtained from bath 1 at 60° C. andat (a) (c) 25 mA/cm², (d)-(f) 50 mA/cm², (g)-(i) 100 mA/cm², (j)-(l) 300mA/cm² and (m)-(o) 500 mA/cm².

FIG. 72 shows SEM of Co—Sm thin films obtained from bath 1 at 50 mA/cm²and at (a)-(b): 25° C., (c)-(d) 40° C. and (e)-(f) 60° C.

FIG. 73 shows SEM of Co—Sm thin films obtained from bath 1 at 50 mA/cm²and at (a)-(c) 25° C., (d)-(f) 40° C. and (g)-(i) 60° C.

FIG. 74 shows dependence of particle size on Sm deposit content atvarious temperatures and CDs.

FIG. 75 shows magnetic hysteresis loops obtained at (a)-(c) 25° C. and(d)-(i) 60° C. and at various CDs from bath 1.

FIG. 76 shows effects of current density and temperature on depositcrystalline structures, particle sizes and magnetic properties.

FIG. 77 shows the effect of the particle size on coercivities offiber-shaped microstructures in Co—Sm alloys.

FIG. 78 shows effect of solution pH on (a) Sm deposit content and (b)current efficiency at 25, 60° C. and various CDs.

FIG. 79 shows XRD patterns of deposits obtained at 10 mA/cm², 25° C. andvarious solution pHs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15Mglycine).

FIG. 80 shows XRD patterns of deposits obtained at 50 mA/cm², 25° C. andvarious solution pHs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15Mglycine).

FIG. 81 shows XRD patterns of deposits obtained at 10 mA/cm², 60° C. andvarious solution pHs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15Mglycine).

FIG. 82 shows XRD patterns of deposits obtained at 50 mA/cm², 60° C. andvarious solution plls. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15Mglycine).

FIG. 83 shows XRD patterns of deposits obtained at 100 mA/cm², 60° C.and various solution pHs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate,0.15M glycine).

FIG. 84 shows XRD patterns of deposits obtained at 300 mA/cm², 60° C.and various solution pHs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate,0.15M glycine).

FIG. 85 shows low magnitude (2,000×) SEM of Co—Sm thin films obtained at(a)-(c) pH 6, (d)-(f) pH 4 and (g)-(i) pH 2 at 25° C. and various CDs.(Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine)

FIG. 86 shows high magnitude (50,000×) SEM of Co—Sm thin films obtainedat (a)-(c) pH 6, (d)-(f) pH 4 and (g)-(i) pH 2 at 25° C. and variousCDs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine).

FIG. 87 shows low magnitude (2,000×) SEM of Co—Sm thin films at (a)-(c)pH 6, (d)-(f) pH 4 and (g)-(i) pH 2 at 60° C. and various CDs. (Bath: 1MSm sulfamate, 0.05M Co sulfate, 0.15M glycine).

FIG. 88 shows high magnitude (50,000×) SEM of Co—Sm thin films obtainedat (a)-(c) pH 6, (d)-(f) pH 4 and (g)-(i) pH 2 at 60° C. and variousCDs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine).

FIG. 89 shows dependence of particle size on Sm deposit content atvarious pHs, temperatures and CDs.

FIG. 90 shows magnetic properties of deposits obtained at 25, 60° C. andvarious pHs. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine).

FIG. 91 shows the effect of rotating rate of RDE on (a) samarium depositcontent and (b) current efficiency at 25° C. (Deposits of 0 rpm rotationrate were obtained from parallel electrode because poor deposits wereobtained by RDE at 0 rpm.).

FIG. 92 shows the effect of rotating rate of RDE on normalized chargesof Sm, Co and H₂ in Co—Sm alloys electrodeposition. (Deposits of 0 rpmrotation rate were obtained from parallel electrode because poordeposits were obtained by RDE at 0 rpm.).

FIG. 93 shows SEM of Co—Sm thin films obtained from bath 1 at 100mA/cm², 25° C. and (a)-(c): no-agitation (non-metallic, obtained fromparallel electrode), (d)-(f) 1000 rpm (Sm=12.5 at %), and (g)-(i) 200rpm (Sm=7.2 at %).

FIG. 94 shows magnetic properties of deposits obtained at 25° C. andvarious rotating rates.

FIG. 95 shows the effect of Sm sulfamate concentration on (a) samariumdeposit content and (b) current efficiency at 25 and 60° C.

FIG. 96 shows the effect of Sm sulfamate concentration on normalizedcharges of Sm, Co and H₂ in Co—Sm alloy electrodeposition.

FIG. 97 shows XRD patterns of deposits obtained at 25° C., 25 mA/cm² andvarious Sm sulfamate concentrations. (Bath: 0.05M Co sulfate, 0.15Mglycine, Sm sulfamate varied from 0.25 to 1M, pH 6).

FIG. 98 shows XRD patterns of deposits obtained at 25° C., 50 mA/cm² andvarious Sm sulfamate concentrations. (Bath: 0.05M Co sulfate, 0.15Mglycine, Sm sulfamate varied from 0.25 to 1M, pH 6).

FIG. 99 shows XRD patterns of deposits obtained at 60° C., 50 mA/cm² andvarious Sm sulfamate concentrations. (Bath: 0.05M Co sulfate, 0.15Mglycine, Sm sulfamate varied from 0.25 to 1M, pH 6).

FIG. 100 shows XRD patterns of deposits obtained at 60° C., 100 mA/cm²and various Sm sulfamate concentrations. (Bath: 0.05M Co sulfate, 0.15Mglycine, 0.25 to 1M Sm sulfamate, pH 6).

FIG. 101 shows the effect of Sm sulfamate concentration on magneticproperties of deposits obtained at 25 and 60° C. (Bath: 0.05M Cosulfate, 0.15M glycine, Sm sulfamate varied from 0.25 to 1M, pH 6).

FIG. 102 shows the effect of glycine concentration on (a) samariumdeposit content and (b) current efficiency at 25 and 60° C.

FIG. 103 shows XRD patterns of deposits obtained at 25° C., 50 mA/cm²and various glycine concentrations. (Bath: 1M Sm sulfamate, 0.05M cobaltsulfate, glycine varied from 0 to 0.5M, pH 6).

FIG. 104 shows XRD patterns of deposits obtained at 60° C., 50 mA/cm²various glycine concentrations. (Bath: 1M Sm sulfamate, 0.05M cobaltsulfate, glycine varied from 0 to 0.5M, pH 6).

FIG. 105 shows the effect of glycine concentration on magneticproperties of electrodeposited Co—Sm thin films obtained at 25 and 60°C.

FIG. 106 shows the effect of NH₄ sulfamate concentration on (a) samariumdeposit content and (b) currentefficiency at 25 and 60° C.

FIG. 107 shows the effect of NH₄ sulfamate concentration on normalizedcharges of Sm, Co and H₂ in Co—Sm alloy electrodeposition.

FIG. 108 shows XRD patterns of deposits obtained from (a) bath 8 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine, 1M NH₄ sulfamate, pH 5.2)and (b) bath 1 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, pH5.7) at 25° C. and various CDs.

FIG. 109 shows XRD patterns of deposits obtained from (a) bath 8 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine, 1M NH₄ sulfamate, pH 5.2)and (b) bath 1 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, pH5.7) at 60° C. and various CDs.

FIG. 110 shows SEM (2,000×) of Co—Sm thin films from bath (a)-(b)without (bath 1) and (c)-(d) with 1M NH₄ sulfamate (bath 8).

FIG. 111 shows SEM (50,000×) of Co—Sm thin films from bath (a)-(c)without (bath 1) and (d)-(l) with 1M NH₄ sulfamate (bath 8).

FIG. 112 shows the effect of NH₄ sulfamate concentration on magneticproperties of electrodeposited Co—Sm thin films obtained at 25 and 60°C. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, NH₄sulfamate varied from 0 to 1M).

FIG. 113 shows the effect of supporting electrolyte on samarium depositat (a) 25 and (b) 60° C.

FIG. 114 shows the effect of supporting electrolyte on currentefficiency at (a) 25 and (b) 60° C.

FIG. 115 shows the effect of supporting electrolyte on normalized chargeof Sm, Co and H₂ at 25° C. and 60° C. in Co—Sm electrodeposition.

FIG. 116 shows SEM of Co—Sm thin films obtained from bath with (a)-(c)no supporting electrolyte, (d)-(f) 1M NH₄ sulfamate, (g)-(i) 1M NH₄Cland (j)-(l) 1M KCl at 25° C. and 25 mA/cm². (Bath: 1M Sm sulfamate,0.05M Co sulfate, 0.15M glycine with different types of supportingelectrolytes) 60° C., 300 mA/cm².

FIG. 117 shows SEM of Co—Sm thin films obtained from bath with (a)-(c)no supporting electrolyte, (d)-(0.1M NH₄ sulfamate, (g)-(i) 1M NH₄C1 and(j)-(l) 1M KCl at 60° C. and 300 mA/cm². (Bath: 1M Sm sulfamate, 0.05MCo sulfate, 0.15M glycine with different types of supportingelectrolytes).

FIG. 118 shows the effect of types of supporting electrolytes onmagnetic properties of electrodeposited Co—Sm thin films obtained at 25and 60° C. (Bath: 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine withdifferent types of supporting electrolytes).

FIG. 119 shows dependence of Bragg angle (2%) of (10.0) and (00.2)planes on Sm deposit content obtained at 60° C.

FIG. 120 shows an experimental flowchart of parametric studies of PCelectrodeposition of Co—Sm alloys.

FIG. 121 shows a schematic of pulse current electrodeposition.

FIG. 122 shows a setup for PC electrodeposition.

FIG. 123 shows the effect of peak current density and solutiontemperature on (a) samarium deposit content and (b) current efficiencyfor DC and PC (T_(on)=0.1 ms, γ=0.1) electrodeposition.

FIG. 124 shows the effect of peak current density and solutiontemperature on normalized charges of Sm, Co and I-1₂ in Co—Sm alloyselectrodeposition by DC and PC (T_(on)=0.1 ms, γ=0.1) electrodeposition.

FIG. 125 shows XRD patterns of deposits obtained from bath 1 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at 25 and 60° C. andvarious PCDs.

FIG. 126 shows SEM of Co—Sm thin films obtained from bath 1 at 25° C.and various PCDs.

FIG. 127 shows SEM of Co—Sm thin films obtained from bath 1 at 60° C.and various PCDs.

FIG. 128 shows magnetic hysteresis loops obtained at (a)-(c) 25° C. and(d)-(i) 60° C. and at various PCDs from bath 1.

FIG. 129 shows effects of peak current density and temperature onmagnetic properties.

FIG. 130 shows the effect of duty cycle on (a) samarium deposit contentand (b) current efficiency (T_(on)=0.1 ms).

FIG. 131 shows the effect of duty cycle on normalized charges of Sm, Coand H₂, in Co—Sm alloys electrodeposition (T_(on)=0.1 ms, γ=0.1).

FIG. 132 shows XRD patterns of deposits obtained from bath 1 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at 25 and 60° C., 500mA/cm² and various duty cycles.

FIG. 133 shows SEM of Co—Sm thin films obtained from bath 1 at 25 and60° C., 500 mA/cm², and various duty cycles.

FIG. 134 shows the effects of duty cycles on magnetic properties.

FIG. 135 shows the effect of frequency on (a) samarium deposit contentand (b) current efficiency (γ=0.1, 25° C.).

FIG. 136 shows the effect of frequency on normalized charges of Sm, Coand H₂ in Co—Sm alloys electrodeposition (γ=0.1, 25° C.).

FIG. 137 shows XRD (left) and SEM (right) of deposits obtained from bath1 at various frequencies (100 mA/cm², γ=0.1, 25° C.).

FIG. 138 shows SEM of Co—Sm thin films obtained from bath 1 at 25° C., 2kHz, γ=0.1 and at (a)-(b) 500 mA/cm² and (c)-(d) 500 mA/cm².

FIG. 139 shows the effects of frequency on magnetic properties at 25° C.

FIG. 140 shows the effect of T_(on) on (a) samarium deposit content and(b) current efficiency (period=100 ms, 25° C.).

FIG. 141 shows the effect of T_(on) on normalized charges of Sm, Co andH₂ in Co—Sm alloys electrodeposition (period=100 ms, 25° C.).

FIG. 142 shows XRD (left) and SEM (right) of deposits obtained from bath1 at various T_(on) (1000 mA/cm², period=1000 ms, 25° C.).

FIG. 143 shows the effects of T_(on) on magnetic properties.

FIG. 144 shows Deposition rates of Sm and Co vs. deposition time in theelectrodeposition of Co—Sm alloys.

Additional advantages of the invention will be set forth in part in thedescription which follows, and in part will be obvious from thedescription, or can be learned by practice of the invention. Theadvantages of the invention will be realized and attained by means ofthe elements and combinations particularly pointed out in the appendedclaims. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the invention, as claimed.

DETAILED DESCRIPTION

The present invention can be understood more readily by reference to thefollowing detailed description of the invention and the Examplesincluded therein.

Before the present compounds, compositions, articles, systems, devices,and/or methods are disclosed and described, it is to be understood thatthey are not limited to specific synthetic methods unless otherwisespecified, or to particular reagents unless otherwise specified, as suchmay, of course, vary. It is also to be understood that the terminologyused herein is for the purpose of describing particular aspects only andis not intended to be limiting. Although any methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, example methods andmaterials are now described.

All publications mentioned herein are incorporated herein by referenceto disclose and describe the methods and/or materials in connection withwhich the publications are cited. The publications discussed herein areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing herein is to be construed as an admissionthat the present invention is not entitled to antedate such publicationby virtue of prior invention. Further, the dates of publication providedherein can be different from the actual publication dates, which mayneed to be independently confirmed.

A. Definitions

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a substrate,” “analloy,” or “a sample” includes mixtures of two or more such substrates,alloys, or samples, and the like.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another aspect includes from the one particular value and/orto the other particular value. Similarly, when values are expressed asapproximations, by use of the antecedent “about,” it will be understoodthat the particular value forms another aspect. It will be furtherunderstood that the endpoints of each of the ranges are significant bothin relation to the other endpoint, and independently of the otherendpoint. It is also understood that there are a number of valuesdisclosed herein, and that each value is also herein disclosed as“about” that particular value in addition to the value itself. Forexample, if the value “10” is disclosed, then “about 10” is alsodisclosed. It is also understood that each unit between two particularunits are also disclosed. For example, if 10 and 15 are disclosed, then11, 12, 13, and 14 are also disclosed.

As used herein, the terms “optional” or “optionally” means that thesubsequently described event or circumstance may or may not occur, andthat the description includes instances where the event or circumstanceoccurs and instances where it does not.

Disclosed are the components to be used to prepare the compositions ofthe invention as well as the compositions themselves to be used withinthe methods disclosed herein. These and other materials are disclosedherein, and it is understood that when combinations, subsets,interactions, groups, etc., of these materials are disclosed that whilespecific reference of each various individual and collectivecombinations and permutation of these compounds may not be explicitlydisclosed, each is specifically contemplated and described herein. Forexample, if a particular compound is disclosed and discussed and anumber of modifications that can be made to a number of moleculesincluding the compounds are discussed, specifically contemplated is eachand every combination and permutation of the compound and themodifications that are possible unless specifically indicated to thecontrary. Thus, if a class of molecules A, B, and C are disclosed aswell as a class of molecules D, E, and F and an example of a combinationmolecule, A-D is disclosed, then even if each is not individuallyrecited each is individually and collectively contemplated meaningcombinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considereddisclosed. Likewise, any subset or combination of these is alsodisclosed. Thus, for example, the sub-group of A-E, B-F, and C-E wouldbe considered disclosed. This concept applies to all aspects of thisapplication including, but not limited to, steps in methods of makingand using the compositions of the invention. Thus, if there are avariety of additional steps that can be performed it is understood thateach of these additional steps can be performed with any specific aspector combination of aspects of the methods of the invention.

It is understood that the compositions disclosed herein have certainfunctions. Disclosed herein are certain structural requirements forperforming the disclosed functions, and it is understood that there area variety of structures that can perform the same function that arerelated to the disclosed structures, and that these structures willtypically achieve the same result.

B. Rare Earth-Transition Metal (RE-TM) Permanent Magnets

RE-TM permanent magnets were developed at 1960's and became a practicalcommercial product at 1970. At that time, the RE-TM permanent magnetsoffered ten times higher coercivity and five times greater energydensity than the best magnets of the 1960's. The maximum energy productfor hard permanent magnetic materials is shown in FIG. 1 [G. J. Long andF. Grandjean, Supermagnets, hard magnetic materials, Kluwer AcademicPublishers, Norwell, Mass., (1991), p3.].

RE-TM permanent magnets of different compositions exhibit a wide rangeof magnetic properties and cost; the research and development of Sm—Coand Nd—Fe-B alloys got more attention among these magnets for theirsuperior performance and practical applications [K. J. Stmat, IEEETrans. Magnetics, Mag-23, 2094, (1987).]. The first practical RE-TMpermanent magnet, sintered SmCo₅, was available about 1970 in the U.S.[M. G. Benz and D. L. Martin, Appl. Phys. Letters, 17, 176, (1970).].Right after SmCo₅, the investigation of quasi-binary intermetallics,RE₂(Co, Fe)₁₇ [A. E. Ray and K. J. Strnat, IEEE Trans. Magnetics, Mag-8,516, (1972); K. J. Strnat, IEEE Trans. Magnetics, Mag-8, 511, (1972).],led to the development of the second generation of REIG permanent magnet—Sm₂Co₁ 7. The first useful Sin₂Co₁₇ was developed in Japan in 1975 [T.Ojima, S. Tomizawa, T. Yoneyama, and T. Hori, Japan. J. Appl. Phys., 16,671, (1977).]. The third generation of RE-TM permanent magnets,Nd₂Fel₄B, was developed by US and Japanese researchers and announced in1983 [7; J. J. Croat, J. F. Herbst, R. W. Lee and F. E. Pinkerton, J.Appl. Phys., 55, 2078, (1984); N. C. Koon and B. N. Das, J. Appl. Phys.,55, 2063, (1984).] and brought new, much higher energy-product permanentmagnets and a promise for cheaper RE-TM permanent magnets. Thedevelopment of RE-TM permanent magnets not only resulted in abreakthrough of high performance magnetic materials but also created newapplications for ferromagnetism materials.

Driven by the increasing interest of high performance permanent magnets,the improvement of RE-TM magnets has been mainly done by theincorporation and substitution of specific elements to RE-TM alloys. Forexample, small substitution of Cu for Co in SmCo₅ leads to theprecipitation of a nonmagnetic phase which increased the coercivity [E.A. Nesbitt, R. H. Willens, R. C. Sherwood, E. Buehler, and J. H.Wernick, Appl. Phys. Letters, 12, 361, (1968).]; the replacement ofparts of Co by Fe in Sm₂Co₁₇ resulted in greater magnetizationsaturation (Ms) [A. E. Ray and K. J. Strnat, IEEE Trans. Magnetics,Mag-8, 516, (1972).] the replacement of 50% of Fe by Co in Nd₂Fe₁₄Bgives higher Curie temperature [R. Grossinger, R. Krewenka, H. Buchner,and H. Harada, J. Phys. (Paris), 49, C8-659, (1988).]. Theseimprovements make RE-TM permanent magnets easier to use for differentkinds of industrial applications (Table 1) and enhances the performanceof these magnetic devices.

Except for the traditional ways of making RE-TM magnets (i.e., bondingand sintering [M. G. Benz and D. L. Martin, Appl. Phys. Letters, 17,176, (1970); M. G. Benz and D. L. Martin, J. Appl. Phys., 43, 4733,(1972); A. E. Ray and K. J. Strnat, IEEE Trans. Magnetics, Mag-11, 1429,(1975).]), new manufacture methods (i.e. mechanical alloying [J. Wecker,M. Katter and L. Schultz, J. Appl. Phys., 69, 6085, (1991); J. Ding, P.G. McCormick and R. Street, J. Alloys Comp., 191, 197, (1993).], nanopowder metallurgy [J. Ding, Y. Liu, P. G. McCormick and R. Street, J.Magn. Magn. Mater., 123, L239, (1993).], and thin film processes -DCsputtering [H. C. Theuerer, E. A. Nesbitt, and D. D. Bacon, J. Appl.Phys., 40, 2994, (1969); S. A. Bendson and J. H. Judy, IEEE Trans.Magnetics, 9, 627, (1973); C. Zhang, R. Liu and G. Feng, IEEE Trans.Magnetics, 16, 1215, (1980); H. S. Cho, J. R. Salem, A. J. Kellock andR. B. Beyers, IEEE Trans. Magnetics, 33, 2890, (1997); R. Andreescu andM. J. O'Shea, I Appl. Phys., 91, 8183, (2002); 22], Rf sputtering [V.Neua and S. A. Shaheen, J. Appl. Phys., 53, 2401, (1982); F. J. Cadieu,S. H. Aly and T. D. Cheung, J. Appl. Phys., 64, 5501, (1988); K. Chen,H. Hegde and F. J. Cadieu, Appl. Phys. Letters, 61, 1861, (1992); T.Numata, H. Kinyama and S. Inokuchi, Appl. Phys., 86, 7006, (1999).], PVD[V. Geiss, E. Kneller and A. Nest, Appl. Phys., A27, 79, (1982); M.Gronau, H. Goeke, D. Schaffler and S. Sprenger, IEEE Trans. Magnetics,Mag-19, 1653, (1983); U. Kullmann, E. Koester and C. Dorsch, IEEE Trans.Magnetics, Mag-20, 420, (1984).], and pulsed laser deposition [V. Neu,J. Thomas, S. Faller, B. Holzapfel and L. Schultz, J. Magn. Magn.Mater., 242-245, 1290, (2002); F. J. Cadieu, R. Rani, and T.Theodoropoulos and Li Chen, J. Appl. Phys., 85, 5895, (1999).]) havebeen studied and developed. The improvement of manufacturing process notonly promotes these high performance devices for traditionalapplications (i.e., automotive, domestic, electronic, aerospace devices)but also for new industrial applications, such as information storage,micro-electromechanical systems (MEMS), and nano-electromechanicalsystems (NEMS) of thin film RE-TM magnets.

TABLE 1 Applications of permanent magnets Application Magnetic Devicesand Products Automotive dc motor drivers, starter motors, windowwinders, wipers, fans, speed meters, alternators Domestic analogues,watches, video recorders, electric clocks, hearing aids, loudspeakersElectronic and sensors, contactless switches, nmr spectrometers, energymeter Instrumentation bearing, transducers, computer printer head,damper Aerospace frictionless bearings, couplings, magnetrons,klystrons, auto compasses Biosurgical dentures, magnetic sphincters,magnetic sutures, cancer cell separators, artifical hearts Informationstorage magneto-optical recording medium, perpendicular recording media,MEMS & NEMS micromotor, actuator, magnetometer, magnetic sensors,magnetic bubble memory

Recent developments of RE-TM magnets have focused on Co—Sm thin films bysputtering on the substrate with Cr underlayer [C. Prados and G. C.Hadjipanayis, J Appl. Phys., 83, 6253, (1998); C. Prados, A. Hernando,G. C. Hadjipanayis and J. M. Gonza'leza, J. Appl. Phys., 85, 6148,(1999); C. Prados and G. C. Hadjipanayis, Appl. Phys. Letters, 74, 430,(1999).]. Proper deposition conditions, alloy composition, and heattreatments increase the coercivity up to 40 kOe which is much higherthan the coercivity of conventional SmCo₅ (about 10 kOe) by otherprocesses. In addition, using Cu as under layer in the sputteringprocess changes Co—Sm alloys from an in-plane to a perpendicularmagnetic anisotropy [J Sayama, T. Asahi, K. Mizutani and T. Osaka, J.Phys. D: Appl. Phys., 37, L1, (2004); J. Sayama, K. Mizutani, T. Asahi,J. Ariake, K. Ouchi, S. Matsunuma and T. Osaka, J. Magn. Magn. Mater.,287, 239, (2005).], which makes it a good candidate for high densityperpendicular recording media (also in terms of its excellent thermalstability and small minimal stable grain size).

A disadvantage of RE-TM permanent magnets to complete in the worldmarket and wide use is their price [G. J. Long and F. Grandjean,Supermagnets, hard magnetic materials, Kluwer Academic Publishers,Norwell, Mass., (1991), pp 585-616.] which is strongly dependent on themanufacture process. Thin film processes, such as sputtering, PVD, andpulsed laser deposition, require a vacuum system and a high puritytarget to avoid impurity in deposits. In addition, the growth rates ofthese processes are slow. Therefore, making Co—Sm thin films by theseprocesses is quite expensive and cannot provide any advantage in costreduction making it difficult for commercialization. In other words, acost effective manufacturing method must be developed to reduce thefabrication cost.

Electrodeposition is a simple, versatile and easily-controlledthin/thick film manufacturing method because of its simple setup, easymaintenance, low temperature operation, and low energy consumption.Compared to sputter, PVD, and other thin film processes, the mostimportant advantage of electrodeposition is low cost. It was indicatedthat PVD process may be as much as ten times more expensive thanelectrodeposition [J. W. Dini, Plat. Surf: Finish., 80, 26, (1993).]. Inaddition, the growth rate of electrodeposition (5-0.1 μm/min) is a lotfaster than other thin film processes (0.1-0.001 μm/min). This giveselectrodeposition an advantage over other “thin film” technologies inthick film deposition which is often required in MEMS devices. With thehelp of masking patterns formed on the seedlayer, deposits of complexshape and geometry can be obtained by the electrodeposition. Therefore,electrodeposition is especially suitable to achieve high aspect ratiodevices and microstructures in LIGA process [A. E. Ray and K. J. Strnat,IEEE Trans. Magnetics, Mag-8, 516, (1972).]. This provideselectrodeposition more versatility and variety making it capable toadapt to various kind of applications. Therefore, usingelectrodeposition should effectively reduce the fabrication cost ofRE-TM thin films and make them more competitive compared to other thinfilm technologies RE metal and alloys have been electrodeposited frommolten salts [T. Iida T. Nohira and Y. Ito, Electrochim. Acta, 48, 901,(2003); T. Iida T. Nohira and Y. Ito, Electrochim. Acta, 48, 901,(2003).[P. Liu, Y. Du, Q. Yang, Y. Tong and G. A. Hope, J. Magn. Magn.Mater., 153, C57, (2006).] and nonaqueous solutions [Y. Sato, H. Ishida,K. Kobayakawa and Y. Abe, Chem. Lett., (8), 1471, (1990); Y. Sato, T.Takazawa, M. Takahashi, H. Ishida and K. Kobayakawa, Plat. Surf Finish.,80, 72, (1993).]. Unfortunately, most of the deposits obtained fromnon-aqueous media have poor magnetic properties, as low coercivity andsaturation magnetization; oxides and hydroxides also be found in somecases after heat treatments [Y. Sato, T. Takazawa, M. Takahashi, H.Ishida and K. Kobayakawa, Plat. Surf Finish., 80, 72, (1993).]. On theother hand, few studies of the electrodeposition of IG-RE alloys fromaqueous solutions have been reported [L. Chen, M. Schwartz, and K. Nobe,in Electrodeposited Thin Films, M. Paunovic and D. A. Scherson, Editors,PV 96-19, p. 239, The Electrochemical Society Proceedings Series,Pennington, N.J. (1996); Schwartz et al., in Magnetic Materials,Processes, and Devices V. Applications to Storage andMicroelectromechanical Systems (MEMS), Romankiw et al., Editors, PV98-20, p. 646, The Electrochemical Society Proceedings Series,Pennington, N.J. (1999); M. Schwartz, N. V. Myung, and K. Nobe, J.Electrochem. Soc., 151, C468, (2004).].

Electrodeposition of RE metals from aqueous solutions is more difficultcompared to non-aqueous solutions, as a result of anticipated vigoroushydrogen evolution at the reduction potentials of RE metals in aqueoussolution. The reduction potentials of RE metals are extremely negative(E°<−2VsitE) [W. M. Latimer, The Oxidation States of the Elements andTheir Potentials in Aqueous Solution, Prentice-Hall, New York, pp.286-295 (1952).],muchlowerthanthereductionpotentialofwater(H₂O+2e⁻20H⁻+1/2H₂, E-0.826V). Therefore, instead of RE metaldeposition, water can decompose first. In addition, RE metal ions wouldbe hydrolyzed at PH>6 and tends to react with dissolved oxygen orhydroxyl ions to form oxide or hydroxide. Therefore, hydroxides andoxides would be deposited instead of RE metal making the deposition ofRE metal from aqueous solution difficult, similar to electrodepositionof Mo, W and V from aqueous solutions. However, Mo, W and V has beenco-electrodeposited with iron group metals from aqueous solution theaddition [L. O. Case and A. Krohn, J. Electrochem. Soc., 105, 512(1958); V. B. Singh, L. C. Singh, and P. K. Tikoo, J. Electrochem. Soc.,127, 590 (1980); M. Schwartz, Unpublished data, 1946; see alsodiscussion in Trans. Electrochem. Soc., 94, 382 (1948); A. Brenner, P.Burkhead, and E. Seegmiller, J. Res. Natl. Bur. Stand., 93, 351 (1947);M. L. Holt and L. E. Vaaler, Trans. Electrochem. Soc., 94, 50 (1948);W.E. Clark and M. L. Holt, Trans. Electrochem. Soc., 94, 244 (1948); M. H.Lietzke and M. L. Holt, Trans. Electrochem. Soc., 94, 252 (1948); W. H.Safranek and L. E. Vaaler, Plating (East Orange, N.J.), 46, 133 (1959);Arcos et al., Magnetic Materials, Processes, and Devices IV.Applications to Storage and Microelectromechanical Systems (MEMS),Romankiw and Herman, Jr., Editors, PV 95-18, p. 563, The ElectrochemicalProceedings Series, Pennington, N.J. (1996); Arcos et al., Plat. SurfFinish., 90 46 (2003).] of an appropriate complexer. Various hypotheseshas been reviewed by Brenner [A. Brenner, Electrodeposition of Alloys,Vol. 2, pp. 400-453, Academic Press, NewYork (1963).] to explain thephenomenon of the co-reduction of these metals, which he referred to as“induced” co-deposition.

In 1947-1948, Schwartz initiated a commercial installation of a Co-Wammonium citrate plating process [J Sayama, T. Asahi, K. Mizutani and T.Osaka, J. Phys. D: Appl. Phys., 37, L1, (2004).]. He found that whensolutions of Co and W salt were mixed, cobalt tungstate precipitateimmediately but dissolved with the addition of citrate. He conjecturedthat both Co²⁺ and W⁶⁺ are present in the same complex withdeportonation of the hydroxycarboxylate portions, resulting in aheteronuclear biscitrate complex.

In 1994, Schwartz initial research of the electrodeposition of IG-REalloys from aqueous solution [M. Schwartz, Unpublished data, UCLA 1994]and tried to extend his idea of complex formation in aqueous Co—W alloyelectrodeposition to IG-RE alloys. Between 1996 and 2004, a series ofstudies of IG-RE alloys from aqueous solutions were reported [L. Chen,M. Schwartz, and K. Nobe, in Electrodeposited Thin Films, M. Paunovicand D. A. Scherson, Editors, PV 96-19, p. 239, The ElectrochemicalSociety Proceedings Series, Pennington, N.J. (1996); Schwartz et al., inMagnetic Materials, Processes, and Devices V. Applications to Storageand Microelectromechanical Systems (MEMS), Romankiw et al., Editors, PV98-20, p. 646, The Electrochemical Society Proceedings Series,Pennington, N.J. (1999); M. Schwartz, N. V. Myung, and K. Nobe, J.Electrochem. Soc., 151, C468, (2004); Myung et al., in FundamentalAspects of Electrochemical Deposition and Dissolution, Matlosz et al.,Editors, PV 99-33, p. 263, The Electrochemical Society ProceedingsSeries, Pennington, N.J. (1999).]. The experimental results indicatedthat RE and IG metals can be co-deposited by addition of appropriatecomplexes, such as glycine and its derivatives, into the solution.Initially, studies were mainly focused on RE mixtures [L. Chen, M.Schwartz, and K. Nobe, in Electrodeposited Thin Films, M. Paunovic andD. A. Scherson, Editors, PV 96-19, p. 239, The Electrochemical SocietyProceedings Series, Pennington, N.J. (1996).] for co-deposition of IG-REalloys [Schwartz et al., in Magnetic Materials, Processes, and DevicesV. Applications to Storage and Microelectromechanical Systems (MEMS),Romankiw et al., Editors, PV 98-20, p. 646, The Electrochemical SocietyProceedings Series, Pennington, N.J. (1999); M. Schwartz, N. V. Myung,and K. Nobe, J. Electrochem. Soc., 151, C468, (2004).]. The researchfocus of this dissertation is on the co-deposition of Co—Sm alloys tofabricate high performance SmCo₅ and Sm₂Co₁₇ permanent magnets, whichpromise much lower costs, more flexibility than existing manufacturingprocesses.

C. Cobalt-Samarium Magnets

Co—Sm magnets are known for magnetocrystalline anisotropy, highcoercivity, and maximum energy products. These characteristics are basedmainly on the intermetallic phases, SmCo₅ and Sm₂Co₁₆. SmCo₅ magnetshave the highest uniaxial anisotropies of any class of magnets, Ku(uniaxial magnetic anisotropy energy coefficient)≅10⁷ J/m³. On the otherhand, Sm₂Co₁₇ magnets exhibit high flux density and Curie temperature.Metastable phases, intermetallic compounds, and crystalline structuresof Co—Sm alloys are the important properties that provide superiorpermanent magnet performance. The unique properties of SmCo₅ and Sm₂Co₁₇magnets will be reviewed.

Different kinds of manufacturing methods for fabricating Co—Sm magnetshave been developed the past 40 years. Bonding and sintering [M. G. Benzand D. L. Martin, Appl. Phys. Letters, 17, 176, (1970); M. G. Benz andD. L. Martin, J. Appl. Phys., 43, 4733, (1972); A. E. Ray and K. J.Strnat, IEEE Trans. Magnetics, Mag-11, 1429, (1975); Z. A. Abdelnour, H.F. Mildrum and K. J. Strnat, IEEE Trans. Magnetics, Mag-16, 1980,(1980)] and mechanical alloying [J. Wecker, M. Katter and L. Schultz, J.Appl. Phys., 69, 6085, (1991); S. K. Chen, J. L. Tsai and T. S. Chin, J.Appl. Phys., 81, 5631, (1997); M. L. Kahn, J. L. Bobet, F. Weil and B.Chevalier, J. Alloys Comp., 334, 285, (2002); J. Zhou, R. Skomski and D.J. Sellmyer, J. Appl. Phys., 93, 6495, (2003)] are the main methods forprocessing large Co—Sm magnets for common applications (e.g.,automotive, domestic, electronic, aerospace devices). Applications forinformation storage, microelectromechanical systems (MEMS), andnanoelectromechanical systems (NEMS) have lead to developments of thinfilm processes such as DC sputtering, RF sputtering, PVD, and pulsedlaser deposition. The preparation of thin film Co—Sm magnets not onlylead to new industrial applications but also improve performance. Thinfilm processes for Co—Sm magnets are disclosed.

1. Co—Sm Alloy System

The potential superior magnetic properties of intermetallic compounds ofSm and Co was the focus of Buschow et al.'s [K. H. J. Buschow and W. A.J. J. Velge, J. Less-Common Met., 13, 11, (1967); K. H. Buschow and A.S. V. D. Goot, J. Less-Common Met., 14, 323, (1967)] investigation ofthe entire concentration range of binary Sm—Co alloys by X-raydiffraction, thermoanalytical and metallographic methods. The phasediagram is shown in FIG. 2. Intermetallic compounds of Sm₃Co, Sm₉Co₄,SmCo₂, SmCo₃, Sm₂Co₇, SmCo₅ and Sm₂Co₁₇ were obtained.

Three eutectics between the phases Sm—Sm₃Co, Sm₉Co₄—SmCo₂ and Sm2Co₁₇—Cowere found. FIG. 3 shows the Co-rich region of the Co—Sm phase diagram[K. J. Strnat, Ferromagnetic materials, Vol 4, E. P. Wohlfarth and K. H.J. Buschow, Editors, Elsevier Science Publishers, New York, (1998), p.143] after den Broeder and Buschow (1972), Perry (1977), and Ray (1986).From the phase diagram, both SmCo₅ and Sm₂Co₁₇ are identified asintermetallic compounds. Sm₂Co₁₇ is a stable phase and its melting pointis about 1335° C. On the other hand, SmCo₅ is a metastable phaseexisting above 805° C. (eutectoid point).

2. Properties of SMCO₅ and SM₂CO₁₇ Magnets

The hexagonal CaCu₅ structure of SmCo₅ [C. Barrett and T. B. Massalski,Structure of metals, Pergamon Press, Oxford, New York, (1980), p 266] isshown in FIG. 4. A smaller hexagonal Co combined within a hexagonal Smin the same plane (layer A and C). A similar hexagonal Co plane rotatedby 30° (layer B) is inserted between two hexagonal Sm planes (layer Aand C).

Single-phase SmCo₅ [R. C. O'Handley, Modern magnetic materials, JohnWiley & Son, Inc., New York, (2000), pp. 496-502] has exhibited roomtemperature coercivity (H_(c)) of 0.72 MA/m (9 kOe), maximum energyproduct of over 200 kJ/m³ (24 MG·Oe) and saturation magnetization (Ms)of 1 T. A high Curie point (T_(c)=685° C.) enables a wide range ofapplications. The high coercivity of SmCo₅ is attributed to reversaldomain nucleation controlled by grain boundaries [J. D. Livingston, AIPConf Proc., 10, 643 (1973)] restricting the mobility of domain wallsleading to high coercivity.

The rhombohedral Th₂Ni₁₇-type structure of Sm₂Co₁₇ [R. C. O'Handley,Modern magnetic materials, John Wiley & Son, Inc., New York, (2000), pp.496-502] is shown in FIG. 5. This structure has the same cobalthexagonal nets as SmCo₅ but with fewer Sm atoms in adjacent layers. Themagnetocrystalline anisotropy of Sm₂Co₁₇ magnets (Ku≅3×10⁶ J/m³) is lessthan SmCo₅ magnets (K≅10⁷ J/m³) as well as its coercivity of 0.68 MA/m(8.5 kOe). Saturation magnetization of 1.2-1.5 T (109-137 emu/g) andCurie temperature (T_(c)) of 810-970° C. are higher, however. The grainsof Sm2Co₁₇ magnets containing fine structures of SmCo₅ pin the domainwalls [P. Campbell, Permanent magnet materials and their application,Cambridge University Press, New York, (1994), pp. 42-43] and can beachieved by proper heat treatment. The pinning mechanism is shown asFIG. 6.

Chemical reduction is usually used to produce Co—Sm powders [P.Campbell, Permanent magnet materials and their application, CambridgeUniversity Press, New York, (1994), pp. 38-45]. Co—Sm magnets can beobtained by sintering Co—Sm powders, molding bonded Co—Sm particles,mechanical alloying, and thin film processes, such as sputter and PVD.After optimization of heat treatment, high coercivities and anisotropicmagnetic properties can be achieved.

3. Thin Film Technology of Co-Sm Magnets

a. DC Sputtering

The first Co—Sm thin film was prepared in 1969 by getter sputtering [H.C. Theuerer, E. A. Nesbitt, and D. D. Bacon, J. Appl. Phys., 40, 2994,(1969)] for comparison with the unusually high coercivity (28.7 kOe,annealed at 400° C.) of sintered Co_(5-x)Cu_(x)Sm alloys found by E. A.Nesbitt et al. [E. A. Nesbitt, R. H. Willens, R. C. Sherwood, E.Buehler, and J. H. Wernick, Appl. Phys. Letters, 12, 361, (1968).]. Thelater obtained Co—Sm thin films, with/without addition of Cu, with veryhigh coercivities were dependent strongly on substrate temperatures(bell-shaped curves), and higher than bulk specimens.

Theuerer et al. reported a maximum coercivity of 20 kOe for SmCo₅obtained with films (400 nm) prepared at 600° C. which is much higherthan the value of only 1 kOe for bulk specimens of the same composition[H. C. Theuerer, E. A. Nesbitt, and D. D. Bacon, J. Appl. Phys., 40,2994, (1969)]. For the Co_(5-x)Cu_(x)Sm (x=1.35) alloys, films (400 nm)prepared at 500° C. had a maximum coercivity of 30 kOe which is greaterthan bulk specimens (12 kOe). Thick films (˜5 um) prepared at 500-600°C. for the respective alloy compositions had lower coercivities (13.3kOe) than thin films (30 KOe, 400 nm) and close to the bulk values (12KOe). Films deposited on crystalline substrates resulted in larger grainsize with lower coercivities.

Bendson and Judy [S. A. Bendson and J. H. Judy, IEEE Trans. Magnetics,9, 627, (1973)] used DC triode sputtering to obtain Co—Sm thin films(100 to 500 nm) at 10⁻³ Torr of Ar on glaze alumina substrates at orabove 600° C. from Co and Sm targets. Saturation magnitization,coercivity and squareness of deposits are shown in FIG. 7. Thesaturation magnitization is reduced by increasing Sm content until themixture becomes paramagnetic between 25 and 30 atomic percent Sm (FIG.7) in agreement with the published value for bulk specimens [R. Lemaire,R. Pauthenet and J. Schweizer, IEEE Trans. Magnetics, Mag-6, 153,(1970)]. In addition, low coercivity is observed over the major range ofcomposition except among 22 at % Sm where extremely high coercivity isfound. In these films, the easy axis lies in the film plane. Addition ofSm apparently results in decreased squareness.

Zhang et al. [C. Zhang, R. Liu and G. Feng, IEEE Trans. Magnetics, 16,1215, (1980)] studied non-crystalline SmCo₅ and Sm_(0.5)MM′_(0.5)Co(MM′: Ce 50%, La 20%, Nd 10%, Pr 10%) thin films (0.7 to 1.4 m) by DCdiode sputtering on a liquid nitrogen cooled glass substrate. Even afterheat treatment at 750° C. for 4 hours, crystalline SmCo₅ was not formed.The coercivity is only about several hundred Oe which is far below 20KOe obtained by Theuerer et al. [H. C. Theuerer, E. A. Nesbitt, and D.D. Bacon, J. Appl. Phys., 40, 2994, (1969)]. On the other hand, due tothe formation of crystalline (β-Co (fcc), saturation magnetization ofSmCo₅ non-crystalline films were about 620-663G (74-79 emu/g) andincreased to 810-880 G (97-105 emu/g) after heat treatment at 600° C.for 2 hours.

Co—Sm thin films (79 at % Co, 21 at % Sm, 24 nm) on Cr (95 nm) werefirst studied in 1994 by DC magnetron sputtering (no heat treatment) [Y.Liu, B. W. Robertson, Z. S. Shan, S. Malhotra, M. J. Yu, S. K.Renukunta, S. H. Liou and D. J. Sellmyer, IEEE Trans. Magnetics, 30,4035, (1994)]. It was found that the volume fraction of the crystallitesdecreased from 91 to 54 at % as the Ar pressure increased from 0.5×10⁻⁴to 3×10⁻⁴ Torr the maximum coercivity of 2.58 kOe was obtained at1.2×10⁻⁴ Torr.

Mizukami et al. [M. Mizukami, T. Abe and T. Nishihara, IEEE Trans.,Magnetics, 33, 2977, (1997)] found that the coercivity of DC sputteredCo—Sm thin film decreased by 50% after exposure to air for 30 hoursbecause Sm was oxidized. A protective Cr layer coating reduced oxidationby forming a Cr/CoSm/Cr structure. Takei et al. [S. Takei, A. Morisakoand M. Matsumoto, J. Appl. Phys., 81, 4674, (1997)] found that thecoercivity of Co—Sm (20 at % Sm) thin films increased linearly with theincreasing Ar pressure. The squareness ratio of 0.92 could be obtainedwith a highly crystallized Cr underlayer (P_(Ar) of 10⁻³ Torr). Thesevalues suggest that an easy axis of magnetization for the CoSm thin filmis in-plane. The coercivity and squareness (1.95 kOe and 0.92,respectively) of CoSm thin film (20 at % Sm) with Cr underlayer in thisstudy is higher than that obtained by Bendson and Judy (0.7 kOe and 0.6)[S. A. Bendson and J. H. Judy, IEEE Trans. Magnetics, 9, 627, (1973)].

The effects of oxidation on the magnetic and electrical properties of DCsputtered CoSm thin films were studied by Cho et al. [H. S. Cho, J.R.Salem, A.J. Kellock and R. B. Beyers, IEEE Trans. Magnetics, 33, 2890,(1997)]. Co—Sm films prepared on Si (100) and quartz glass by DCmagnetron sputtering of different composition and substrate temperatureswere characterized. The results are summarized in FIG. 8. Co—Sm filmsdeposited at room temperature were non-crystalline, and the coercivityincreased from 20 to 300 Oe and the magnetization saturation decreasedfrom 1400 to 500 emu/cm³ (154 to 60 emu/g or 1.76 to 0.63 T) withincreasing Sm deposit content from 0 to 28 at %. With increasedsubstrate temperature from 25 to 350° C., the coercivity increased from200 to 8000 e and the magnetization saturation decreased from 500 to 380emu/cm³ (60 to 46 emu/g or 0.63 to 0.48 T).

Cho et al. believed that these different behaviors depend on the extentof oxidation in the film especially at high substrate temperatures [H.S. Cho, J. R. Salem, A. J. Kellock and R. B. Beyers, IEEE Trans.Magnetics, 33, 2890, (1997)]. More than 10 at % oxygen was present insputtered deposits at room temperature, and the amount of oxygenincreased with substrate temperature. TEM results indicated that Co—Smthin films deposited at 360° C. were multiphase mixtures of Sm₂O₃ andCo-enriched phases rather than a simple homogeneous Co—Sm phase.

In 1998 Liu et al. [Y. Liu, R. A. Thomas, S. S. Malhotra, Z. S. Shan, S.H. Liou and D. J. Sellmyer, J. Appl. Phys., 83, 6244, (1998)] studiedphase formation and magnetic properties of Co—Sm thin films (DCmagnetron sputtering) by increasing thickness with a Cr cover layer asMizukami et al [M. Mizukami, T. Abe and T. Nishihara, IEEE Trans.,Magnetics, 33, 2977, (1997)] compared to his previous work [Y. Liu, B.W. Robertson, Z. S. Shan, S. Malhotra, M. J. Yu, S. K. Renukunta, S. H.Liou and D. J. Sellmyer, IEEE Trans. Magnetics, 30, 4035, (1994)]. Itwas found that for deposits (19 at % Sin, 360 nm) obtained at Arpressure of 2×10⁻⁴ Torr then annealed at 600° C. has SmCo₅ phases and anextremely high coercivity of 45 kOe. TEM showed a new phase SmCo₃ (22 at% Sm) was formed when the film was annealed at 500° C.

Prados et al [C. Prados and G. C. Hadjipanayis, J. Appl. Phys., 83,6253, (1998); C. Prados and G. C. Hadjipanayis, Appl. Phys. Letters, 74,430, (1999); C. Prados, A. Hernando, G. C. Hadjipanayis and J. M.Gonzaleza, J. Appl. Phys., 85, 6148, (1999)] sputtered Sm(Co, Ni, Cu)thin films (500 nm) on Cr underlayers (300 nm) on water cooled Si topromote a c-axis texture along the in-plane direction in order toincrease their in-plane magnetic anisotropy. After films obtained fromDC magnetron sputtering, the thin films were annealed in a vacuumgreater than 10⁻⁵ Torr at 400 to 650° C. for 30 min. Crystallization ofthe non-crystalline magnetic films (obtained at room temperature)produced a huge enhancement of coercivity (from 100 to more than 40kOe). High angle XRD patterns indicate that the Cr underlayers grew witha (110) texture, and the Sm(Co, Ni, Cu) thin films were non-crystallineas deposited. After annealing, the (111) plane of SmCo₅ appeared andoptimum samples indicated a nanocrystalline structure (particle size of10 nm).

After Liu and Prados showed that the Cr underlayer plays a significantrole in the magnetic properties of Co—Sm thin films, Takei et al. [S.Takei, A. Morisako and M. Matsumoto, J. Appl. Phys., 87, 6968, (2000)]worked on the effect of different kinds of underlayers, such as Cr, Mo,W, W/Cr and Al. The coercivity of the films with Cr and Mo underlayerwere larger than 3 kOe for underlayers thicker than 100 nm. Thesquareness of the films with Cr and Mo underlayers were higher than 0.85and 0.94, respectively. The result indicated that both Cr and Mo aresuitable for SmCo films with in-plane magnetic anisotropy. Forultra-thin Co—Sm films (2.5 nm) deposited on Cr underlayer (100 nm) onCorning #7059 glass the XRD pattern indicated that the Sm—Co layercrystallized by substrate heating with coercivity higher than 3 kOe.Substrate heating during deposition was effective in preparing ultrathinSm—Co thin films with higher coercivity.

There have been many in-plane magnetic anisotropy studies of Co—Sm thinfilms but few of perpendicular magnetic anisotropy. Recently, Sayama etal. [J. Sayama, T. Asahi, K. Mizutani and T. Osaka, J. Phys. D: Appl.Phys., 37, L1, (2004); J. Sayama, K. Mizutani, T. Asahi, J. Ariake, K.Ouchi, S. Matsunuma and T. Osaka, J. Magn. Magn. Mater., 287, 239,(2005)] DC sputtered CoSm thin films [Co(0.41 nm)/Sm(0.31 nm)]₃₅ on Cuunderlayer (100 nm) on a glass substrate at various temperatures.Coercivity increased rapidly between 325-345° C. and was greater in theperpendicular direction than the in-plane direction. The Co/Sm laminatestructure on Cu underlayer was the key in the crystallization of SmCo₅with its c-axis perpendicular to the film plane. The perpendicularmagnetic anisotropy was further improved by reducing the surfaceroughness of the Cu underlayer.

Takei et al. [S. Takei, A. Morisako and M. Matsumoto, J. Magn. Magn.Mater., 272-276, 1703, (2004)] obtained similar results to Sayama et al.[J. Sayama, T. Asahi, K. Mizutani and T. Osaka, J. Phys. D: Appl. Phys.,37, L1, (2004); J. Sayama, K. Mizutani, T. Asahi, J. Ariake, K. Ouchi,S. Matsunuma and T. Osaka, J. Magn. Magn. Mater., 287, 239, (2005)] andfound that the Co—Sm layer with (001) orientation was crystallized ontop of the (111) Cu orientation underlayer and perpendicular coercivityof the film was about 9.6 kOe with substrate temperatures about 300° C.

b. RF-Sputtering

Cadieu et al. [F. J. Cadieu, S. H. Aly and T. D. Cheung, J. Appl. Phys.,53, 2401, (1982)] deposited Co—Sm thin films (1.61 lam) deposited on anAl₂O₃ substrate by RF-sputtering. The composition of the Co—Sm thinfilms were close to the composition SmCo₅ and Sm₂Co₁₇. Hysteresis loopsfor various Sm deposit content are shown in FIG. 9.

The low saturation magnitization measured perpendicular to the filmplane and the XRD patterns indicated that the c-axis is stronglyoriented in the film plane direction. This result is similar to thecrystalline Co—Sm thin films made by DC sputtering onto heated substrateor by crystallization (annealing) of a noncrystalline deposit. Theenergy product measured in the in-plane direction was lower than bulkspecimens which might be due to the random orientation of the c-axis inthe film plane.

Velu et al. [E. M. T. Velu and D. N. Lambeth, J Magn. Magn. Mater., 69,5175, (1991)] studied the Co—Sm thin films with/without Cr underlayer on7059 Coming glass and NiP coated Al substrates. The coercivity of theCoSm thin films was higher for Cr underlayers deposited at 10⁻² Torr Arpressure. The coercivity decreased with higher substrate temperature(>300° C.) which might due to the crystallographic texturetransformation of Cr from <110> to <200> orientation. A maximumcoercivity of 2.4 kOe and squareness of 1 were obtained for CoSm thinfilms (14nm) under optimal conditions.

Chen et al. studied the induced anisotropy [K. Chen, H. Hegde and F. J.Cadieu, Appl. Phys. Letters, 61, 1861, (1992)] and different other typesof anisotropy [K. Chen, H. Hegde, S. U. Jen and F. J. Cadieu, J Appl.Phys., 73, 5923, (1993)] in RF sputtered non-crystalline Sm—Co thinfilms on water cooled polycrystalline Al₂O₃ substrates. An in-planemagnetic field was applied during RF sputtering. Both in-plane andperpendicular anisotropy were found depending on the sputteringconditions. Three different sources of anisotropy can be distinguishedin these films. The in-plane anisotropy was explained as directionalpair ordering; perpendicular anisotropy was only observed for filmsdeposited through sputtering at room temperature; a much largeranisotropy was observed at higher deposition temperatures with the easyaxis in the film plane.

Neu et al. [V. Neua and S. A. Shaheen, J. Appl. Phys., 86, 7006, (1999)]RF-sputtered SmCo₅ and Sm(CoFeCuZr)₇ thin films (1 μm) on heatedpolycrystalline Al₂O₃ substrates. With increased Sm deposit content,Sm—Co thin films transformed from the TbCu₇-type to the CaCu₅-typestructure at around 17 at % Sm in agreement with the stoichiometricSmCo₅ (16.7 at %). With increasing Sm content, the c-axis of SmCo₅preferred to lie on the film plane. The morphology showed larger andmore elongated grains with increasing Sm content which might be due to ahigher surface mobility of Sm-rich samples. Higher Sm content resultedin higher coercivity and lower Mrperpendicular/Mr parallel values (FIG.10), the result of crystallization of SmCo₅.

c. PVD

Geiss et al. [V. Geiss, E. Kneller and A. Nest, Appl. Phys., A27, 79,(1982)] studied non-crystalline Sm_(100-x)Co_(x) (70<x<90) thin films(150 nm) prepared by vapor deposition on flat glass substrates at roomtemperature. A magnetic field of 500 Oe was applied parallel to the filmplane during evaporation. After deposition, specimens were aged atvarious temperatures. The easy axis of magnetization lay on film planeand deposits appeared non-crystalline magnets. The coercivity variedbetween 30 to 3000 Oe, depending on the composition, temperature andheat treatment. Aging of any sample at temperatures below thecrystallization temperature resulted in a decrease in coercivity.

Gronau et al. [M. Gronau, H. Goeke, D. SchUffler and S. Sprenger, IEEETrans. Magnetics, Mag-19, 1653, (1983)] prepared non-crystallineSm_(1-x)Co_(x) (0.67<x<0.91) thin films (10 to 350 nm) byflash-evaporation of SmCo-alloy powder on glass substrates. Saturationmagnitization decreased linearly with increasing Sm content with thesame slope as the crystalline material, but differences were about 10%smaller for the non-crystalline phase in agreement with the results ofDC sputtered deposits by Bendson and Judy [S. A. Bendson and J. H. Judy,IEEE Trans. Magnetics, 9, 627, (1973)]. For x=0.67 (SmCo₂) crystals werenonmagnetic with Ms nearly zero. The coercivity increased, reached amaximum of 53 kA/m (650 Oe) at x=0.74, then decreased. They concludedthat there was little difference for films prepared by evaporation onheated substrate or annealed at the same temperature.

Following Geiss [K. Chen, H. Hegde, S. U. Jen and F. J. Cadieu, J Appl.Phys., 73, 5923, (1993)] and Gronau [M. Gronau, H. Goeke, D. SchUfflerand S. Sprenger, IEEE Trans. Magnetics, Mag-19, 1653, (1983)], Kullmannet al. [U. Kullmann, E. Koester and C. Dorsch, IEEE Trans. Magnetics,Mag-20, 420, (1984)] prepared non-crystalline Sm_(100-x)Co_(x) (75<x<90)thin films (100 nm) by PVD to obtain high density longitudinalrecording. With increasing Sm content, the coercivity increased from 30to 100 kA/m (375 to 1250 Oe). The saturation magnetization was decreasedwith decreased Sm content.

The recording performance showed an improvement in recording density andsignal-to-noise ratio compared to traditional longitudinal recordingmedia.

4. Electrodeposition of Co-RE (Rare Earth) Alloys

a. Electrodeposition of Co-RE Alloys from Non-Aqueous Solutions

In 1953, Moeller et al. [T. Moeller and P. A. Zimmerman, J. Am. Chem.Soc, 75, 3940, (1953); T. Moeller and P. A. Zimmerman, Science, 120,539, (1954)] dissolved anhydrous yttrium acetate, neodymium bromide andlanthanum nitrate in anhydrous ethylenediamine and monoethanolamine toobtain yttrium, neodymium and lanthanum. Electrolyses of ethylenediaminesolutions gave metallic cathode deposits with all salts tested, butdeposits were not obtained from monoethanolamine solutions due to lowsolubility and conductivities. All deposits exhibited rare-earth metalproperties, such as oxidation in air or in water and hydrogen evolutionfrom hydrochloric acid solution.

Increased interest in higher performance Co—Sm magnets (SmCo₅ andSm₂Co₁₇) lead to studies of the electrodeposition of Co-Sin alloys fromnon-aqueous media since aqueous electrodeposition of Co—Sm alloys wasextremely difficult, if not impossible, due to excessive hydrogenevolution. [Y. Sato, H. Ishida, K. Kobayakawa and Y. Abe, ChemistryLetter, 1471 (1990); T. Lida, T. Nohira and Y. Ito, Electrochim. Acta,48, 901, (2003); T. Lida, T. Nohira and Y. Ito, Electrochim. Acta, 48,2517, (2003); P. Liu, Y. Du, Q. Yang, Y. Tong and G. A. Hope, J. Magn.Magn. Mater., 153, C57, (2006)]

Sato et al. [Y. Sato, T. Takazawa, M. Takahashi, H. Ishida and K.Kobayakawa, Plat. Surf Finish, 72, 80, (1993); Y. Sato, H. Ishida, K.Kobayakawa and Y. Abe, Chemistry Letter, 1471 (1990)] electrodepositednon-crystalline Sm—Co thin films from a formamide solution containinganhydrous samarium and cobalt chloride. The deposits were confirmed asmetallic by XPS. The results suggested that the deposit contains Co-richcompounds such as Sm₂Co₁₇ and SmCo₃, which show ferromagnetism. However,after deposits were heat treated at 600° C. for 3 hours, cobalt oxideswere found in the specimens. The magnetic properties of deposits afterannealing did not improve. The highest coercivity before heat treatmentwas about 90 Oe and after heat treatment at 600° C. for 3 hours about562 Oe.

In 2003, Iida et al. studied the electrodeposition of Sm—Co alloys at aCo cathode in a molten LiCl—KCl—SmCl₃ system [T. Lida, T. Nohira and Y.Ito, Electrochim. Acta, 48, 901, (2003)] at 723 K. In addition, a moltenLiCl—KCl—SmCl₃—CoCl₂ system [T. Lida, T. Nohira and Y. Ito, Electrochim.Acta, 48, 2517, (2003)] at 450° C. using a Cu substrate also had beenstudied. Phases of the deposited Sm—Co alloys could be controlled by thepotential. Sm₂Co₁₇, SmCo₃, SmCo₂, and Li_(x)Sm₄Co₆ were found at thepotentials of 1.4, 0.8, 0.3 and 0.05V (vs. Li⁺/Li). However, the depositrate was slow (0.004-5 um/hr) and magnetic properties were not measured.

Recently, in 2006, Liu et al. [P. Liu, Y. Du, Q. Yang, Y. Tong and G. A.Hope, J. Magn. Magn. Mater., 153, C57, (2006)] codeposited Sm—Conon-crystalline films in a urea-acetamide-NaBr-MCl melt (M=Sm or Co).They found that the reduction of Co is irreversible and Sm cannot bereduced alone in these melts and applied the idea of a polynuclearcomplex mechanism as proposed by Schwartz et al [N. V. Myung, M.Schwartz, and K. Nobe, in Fundamental Aspects of ElectrochemicalDeposition and Dissolution, M. Matlosz, D. Landolt, R. Aogaki, Y. Sato,and J. B. Talbot, Editors, PV 99-33, p. 263, The Electrochemical SocietyProceedings Series, Pennington, N.J. (1999).] in the glycine aqueoussystem. The Sm—Co films were non-crystalline as deposited, andintermetallic Sm—Co phases were found after heat treatment at 900° C.Unfortunately, the saturation magnetization of a deposit of 3.3 at % Smis only 2.9 emu/g (before heat treatment) which is too low compared toDC sputtering (143 emu/g) for a similar alloy composition. The highestcoercivity of deposits after heat treatment (900° C., 3 hr) was 180 Oe(60 at % Sm) with saturation magnetization of 1.66 emu/g.

b. Electrodeposition of IG-W, Mo and V Alloys

Brenner suggested that although metals with extreme negative reductionpotentials, such as W, Mo and V, cannot be deposited from aqueous mediaindividually, co-deposition with the iron group metals can be achieved.Review of representative investigations of these alloys follow:

c. IG-W Alloys

Holt and his student [J. Seim and M. L. Holt, Trans. Electrochem. Soc.,95, 205 (1949); D. W. Ernst, R. F. Amlie and M. L. Holt, J. Electrochem.Soc., 102 (8), 461 (1955); D. W. Ernst and M. L. Holt, Ibid., 105 (11),686 (1958).] co-electrodeposited IG-W alloys from ammoniacal solutionscontaining organic hydroxyl acids, such as citric, tartric, and malicacid. Hydroxyl acids, which are known as good complexing agents,increased current efficiency and tungstate solubility to obtain smoothIG-W deposits. The reduction of the tungstate was suggested due to thecatalysis of atomic hydrogen reduction by a two-step reductionhypothesis.

Brenner et al. [A. Brenner, P. Burkheard and E. Seegmiller, J. Res. NBS,94, 351 (1947).] developed a codeposition process of W and iron groupalloys from aqueous ammoniacal solutions (˜pH8.5) containing appropriatemetal salts (sodium tungstate and 1G (iron group)-chloride orIG-sulfate) and certain hydroxyl-organic acids (citric acid, tartaricacid, hydroxyacetic acid, malic acid, gluconic acid). They concludedthat the W ion concentration is the most important variable affecting Wdeposit content, which increased and reached a limit with increasing Wconcentrations. The maximum W deposit content of Co—W and Fe—W alloyswas about 23 to 32 at %, and about 12 at % for Ni—W alloys. W depositcontent increased with CD, but did not significantly change withtemperature. However, current efficiency increased considerably withincrease in temperature.

Schwartz (1948) developed a commercial Co—W plating process using anammoniacal citrate bath [M. Schwartz, unpublished data, 1948-55; seealso discussion in Trans. Electrochem. Soc., 94, 382 (1948)]. He foundthat when the Co and. WO₄ ²⁻ salt solutions are mixed, a cobalttungstate precipitate forms which dissolves with addition of citrate.His experimental results lead him to conjecture that both Co(I1) andW(VI) are coordinated in the same complex with deprotonation of thecarboxylate forming a heteronuclearbiscitrato complex [M. Schwartz andK. Nobe, Trans. Electrochem. Soc., 1, 103 (2006)].

Recently, Gileadi and his coworkers [Younes and E. Gileadi, J.Electrochem. Soc., 149, C100, (2002); Younes-Metzler, L. Zhu andE.Gileadi, Electrochim. Acta, 48, 2551, (2003)] obtained high W deposit(˜67 at %) content Ni—W alloys from non-ammonia plating baths. However,current efficiency was reduced dramatically. The formation of aheteronuclear Ni—W monocitrato complex, [Ni(WO₄)(cit)(H)]²⁻ was proposedas to co-deposition of the Ni—W alloy.

d. IG-Mo Alloys

Holt and co-workers [L. E. Vaaler and M. L. Holt, Trans. Electrochem.Soc. 90, 43 (1946); L. E. Vaaler and M. L. Holt, Ibid., 94, 50 (1948);W. E. Clark and M. L. Holt, Ibid., 94, 244 (1948); M. H. Lietzke and M.L. Holt, Ibid., 94, 252 (1948); R. F. McElwee and M. L. Holt, J.Electrochem. Soc., 99 (2), 48 (1952).] extended their co-depositionstudies of IG-W alloys to IG-Mo alloys from equivalent solutions. HullCells were initially used to determine operating conditions, such as pH,temperature, CD ranges for bright, metallic deposits. Similar to IG-Wco-deposition, deposit Mo contents depended on the co-depositing IGmetal with Fe>Co>Ni. Current efficiencies decreased with increased Mocontent: Ni>Co>Fe. Complexation with citrate and tartrate were favoredfor Ni—Mo codeposition with malate (and malic acid) and glycolic acidsfor Co—Mo. Sodium citrate was superior to citric acid or ammoniumcitrate.

Landolt and Podlaha have published a series of papers [E. J. Podlaha andD. Landolt, J. Electrochem. Soc., 143, 885, (1996); E. J. Podlaha and D.Landolt, J. Electrochem. Soc., 143, 893, (1996); E. J. Podlaha and D.Landolt, Electrochem. Soc., 144, 1672, (1997)] on the codeposition ofNi-Mo alloys using rotating cylinder electrodes from the platingsolutions of NH₃, C₆H₅Na₃O₇.2H₂O, Na₂MoO₄.2H₂O, and NiSO₄.6H₂O. Alloycomposition was affected by CD, electrode rotation rate, solutiontemperature, and species concentration, and Ni—Mo alloys of Mo contentin excess of 50 wt % have been deposited [E. J. Podlaha and D. Landolt,J. Electrochem. Soc., 143, 885, (1996)]. For electrolytes of low Moconcentration in the present of excess Ni concentration, Mo contentincreased with increased electrode rotation rate and decreased withincreased CDs. On the other hand, for electrolytes of low Niconcentration in the present of excess Mo concentration, Mo contentswere independent of convection. A steady-state mathematical model wasdeveloped to predict the codeposition of Ni—Mo alloys [E. J. Podlaha andD. Landolt, J. Electrochem. Soc., 143, 893, (1996)]. This model assumethat both Ni and Mo can complex with citrate in alkaline solutions, butthe formation constant of Mo-citrate constant is much smaller than thatof the Ni-citrate complex. The model predictions were in agreement withthe observed trends in the experimental data [E. J. Podlaha and D.Landolt, J. Electrochem. Soc., 143, 885, (1996)]. Rotating cylinderelectrodes of NiMo, CoMo, and FeMo alloys were electrodeposited for Mosolution concentrations much lower than the iron group species [E. J.Podlaha and D. Landolt, Electrochem. Soc., 144, 1672, (1997)]. Modeposit content was higher in CoMo than NiMo and FeMo deposits due to alower deposition rate of Co than Ni and Fe.

e. IG-V Alloys

Arcos et al. [C. Arcos, M. Schwartz and K. Nobe, AVG′, Electrochem.Soc., 95-15, 193, (1994); M. Schwartz, C. Arcos and K. Nobe, Plat. SurfFin., 90, (6), 46, (2003)] reported the co-deposition (citrate baths) ofbinary and ternary alloys of the iron group metals and vanadium (i.e.Fe—V, Ni—V, Co—V, Co—Ni—V, Ni—Fe—V and Co—Fe—V) by DC and PC. Generally,vanadium deposit content increased with increase in pH (from 5.5 to 7.5)and increased CD (from 5 to 10 A/cm²). In binary alloys, at pH 7, Vcontent decreased as: Fe>Ni>Co. Only Fe—V was obtained at pH below 7.For ternary alloys, the Co and V content increased and Fe decreased byincreased pH for Co—Fe—V alloys. Convective mass transport and longeroff time (PC) resulted in increased V deposit content. Co-depositedCo—Fe—V alloys had higher saturation magnetization compared to Ni—Fe(Perrnalloy type alloys) deposits for both DC and PC. The corrosionresistance of the deposits decreased as: Ni—Fe (DC)>Co—Fe—V (PC)>Co—Fe—V(DC)>Co—Fe (DC).

You et al. [B. Y. Yoo, M. Schwartz, and K. Nobe, Electrochim. Acta, 50,4335, (2005)] investigated the electrodeposition of IG-V binary alloysfrom citrate solutions. Addition of NH₃ and increasing pH lead toincrease in V deposit content, but non-metallic deposits were obtainedat solution pH>7. Increasing CD resulted in a linear decrease of Vdeposit content and a sharp decrease of current efficiency. In general,the V deposit content increased as follows: Ni (1 wt %)<Fe (2 wt %)<<Co(4 wt %).

5. Electrodeposition of Co-RE Alloys from Aqueous Solutions

Compared to non-aqueous investigations, few studies of the codepositionof Co—Sm alloys from aqueous solution have been reported. Most of thesestudied were done by the UCLA group [L. Chen, M. Schwartz, and K. Nobe,in Electrodeposited Thin Films, M. Paunovic and D. A. Scherson, Editors,PV 96-19, p. 239, The Electrochemical Society Proceedings Series,Pennington, N.J. (1996); M. Schwartz, F. He, N. Myung, and K. Nobe, inMagnetic Materials, Processes,and Devices V. Applications to Storage andMicroelectromechanical Systems (MEMS), L. T. Romankiw, S. Krongelb, andC. H. Ahn, Editors, PV 98-20, p. 646, The Electrochemical SocietyProceedings Series, Pennington, N.J. (1999); N. V. Myung, M. Schwartz,and K. Nobe, in Fundamental Aspects of Electrochemical Deposition andDissolution, M. Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J. B.Talbot, Editors, PV 99-33, p. 263, The Electrochemical SocietyProceedings Series, Pennington, N.J. (1999); M. Schwartz, N. V. Myung,and K. Nobe, J. Electrochem. Soc., 151, C468, (2004).]. Zangarisynthesized Sm—Co nanoparticles [J. Zhang, P. Evans, and G. Zangari, J.Magn. Magn. Mater., 283, 89, (2004).] by single short pulseelectrodeposition from the solution proposed by Schwartz et al. [M.Schwartz, N. V. Myung, and K. Nobe, J. Electrochem. Soc., 151, C468,(2004).].

In 1996, Chen et al. [L. Chen, M. Schwartz, and K. Nobe, inElectrodeposited Thin Films, M. Paunovic and D. A. Scherson, Editors, PV96-19, p. 239, The Electrochemical Society Proceedings Series,Pennington, N.J. (1996).] published the first study of IG-RE alloys fromaqueous solution. Electrodepositions was carried out at room temperatureand pH 4 from the plating solution containing RE mixtures, Co, Fe or Nichloride salts, and various addition agents; soluble anodes were used.In direct current (DC) electrodeposition, it was noted that RE was notfound in the deposits from the solutions of pH<4. RE deposit content(Co-RE and Ni-RE) increased with increasing current density (CD) from 5to 20 mA/cm². RE deposit content was higher for Fe-RE than Ni-RE andCo-RE. In pulsed current (PC) electrodeposition, higher temperatures andcobalt concentrations resulted in lower RE deposit content. Forcodeposition of metallic IG-RE alloys, specific addition agents (i.e.aminocarboxylates) in the plating solution were required.

In 1998, Schwartz et al. [M. Schwartz, F. He, N. Myung, and K. Nobe, inMagnetic Materials, Processes,and Devices V. Applications to Storage andMicroelectromechanical Systems (MEMS), L. T. Romankiw, S. Krongelb, andC. H. Ahn, Editors, PV 98-20, p. 646, The Electrochemical SocietyProceedings Series, Pennington, N.J. (1999).] used plating solutionscontaining 0.3M RE metal ions (i.e. La, Ce, Nd, Gd and RE mixtures),0.12M IG ions, 0.36M complexant (e.g., glycine, alanine and serine), 1MNH₄Cl and 0.5M H₃BO₃ to obtain IG-RE alloys at room temperature. In DCelectrodeposition, it was found that the addition of NH₄Cl improvedsolution stability and deposit appearance. RE deposit content decreasedin the order: glycine>serine>alanine. With glycine, the RE depositcontent increased: Co<Fe<Ni. PC electrodeposition extended the effectivepeak CD range for metallic deposits. Crack density seemed to be directlyrelated to the deposit RE content.

In 1999, Myung et al. [N. V. Myung, M. Schwartz, and K. Nobe, inFundamental Aspects of Electrochemical Deposition and Dissolution, M.Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J. B. Talbot, Editors, PV99-33, p. 263, The Electrochemical Society Proceedings Series,Pennington, N.J. (1999).] used chloride-based plating solutionscontaining 0.3M RE ions (i.e. Nd or Sm), 0.12M IG ions (i.e. Co and Ni),0.36-0.72M glycine and 1M NH₄Cl to obtain 10-RE alloys at roomtemperature. 0-0.4M DMAB (dimethylamineborane) was added to solutions toobtain ternary RE-IG-B alloys. Soluble IG served as anodes, and brassand stainless steel panels served as cathode substrates. MetallicNd—Ni—B alloys were electrodeposited at pH6 and CD<40 mA/cm². IncreasedCD led to increased Nd content, decreased B content and currentefficiency. Increasing glycine/Ni ion concentration decreased Nd contentand increased current efficiency. Metallic Sm—Co and Sm—Co—B alloys wereobtained at pH 4-6.5, CD<40 mA/cm². In the absence of DMAB in solutions,Sm content increased with increased CD; in the presence of DMAB, theopposite trend was observed. The crystal structures of Sm—Co and Sm—Co—Balloys were hexagonal closed pack (hcp) (CD<10 mA/cm²) ornon-crystalline (CD>10 mA/cm²) Deposit grain size reduced from 128 to 38nm by increased CD from 5 to 30 mA/cm².

In 2004, Schwartz et al. [M. Schwartz, N. V. Myung, and K. Nobe, J.Electrochem. Soc., 151, C468, (2004).] used chloride- or sulfamate-basedplating solutions containing 0.3 or 0.9M RE metal ions (i.e. Ce, Nd, Gdand Sm), 0.12M IG ions (i.e. Fe, Co and Ni), 0.36M complexant (e.g.,glycine, alanine and serine), 1M NH₄ ions (i.e. NH₄Cl or NH₄NH₇SO₃) toobtain IG-RE alloys at room temperature with soluble IG or insoluble Tiserving as anodes. The result agreed with previous studies [L. Chen, M.Schwartz, and K. Nobe, in Electrodeposited Thin Films, M. Paunovic andD. A. Scherson, Editors, PV 96-19, p. 239, The Electrochemical SocietyProceedings Series, Pennington, N.J. (1996); M. Schwartz, F. He, N.Myung, and K. Nobe, in Magnetic Materials, Processes, and Devices V.Applications to Storage and Microelectromechanical Systems (MEMS), L. T.Romankiw, S. Krongelb, and C. H. Ahn, Editors, PV 98-20, p. 646, TheElectrochemical Society Proceedings Series, Pennington, N.J. (1999); N.V. Myung, M. Schwartz, and K. Nobe, in Fundamental Aspects ofElectrochemical Deposition and Dissolution, M. Matlosz, D. Landolt, R.Aogaki, Y. Sato, and J. B. Talbot, Editors, PV 99-33, p. 263, TheElectrochemical Society Proceedings Series, Pennington, N.J. (1999).]that the RE deposit content increased with the increasing CD andsolution pH. The Sm deposit content ranked as: Fe>Ni=Co. Metallic Co—Smdeposits did not extend beyond CD=400 mA/cm² resulted in maximum Smdeposit content of 8 at %. Aminoacids were found to be effectivecomplexing agents for the codeposition of RE alloys; glycine resulted inhigher RE deposit contents than serine and alanine(glycine>serine>alanine) at room temperature. A mechanism for thecodeposition of IG-RE alloys was proposed involving hetero-nuclearglycinato coordination complexes as a result of the zwitterioniccharacteristics of glycine. Surface adsorbed H atoms and/or directelectron transfer might result in step-wise reduction of the depositingmetals.

In 2004, Zhang et al. [J. Zhang, P. Evans, and G. Zangari , J. Magn.Magn. Mater., 283, 89, (2004).] used the plating solution proposed bySchwartz et al. [N. V. Myung, M. Schwartz, and K. Nobe, in FundamentalAspects of Electrochemical Deposition and Dissolution, M. Matlosz, D.Landolt, R. Aogaki, Y. Sato, and J. B. Talbot, Editors, PV 99-33, p.263, The Electrochemical Society Proceedings Series, Pennington, N.J.(1999).] to synthesize Sm—Co nanoparticles by single short pulseelectrodeposition. Nanoparticle composition was a function of pulseamplitude (PCD 0.1-1.5 A/cm²) and pulse duration (T_(on) 5-100 ms); therelative atomic percent of Sm, defined as Sm/(Sm+Co), increased withincreasing PCD and decreasing T_(on) XRD and XPS data indicate that hcpCo—Sm metallic alloys mixed with metal oxides have been obtained. Theoxygen atomic ratio O/(Sm+Co+O) was a function of T_(on). IncreasingT_(on) decreased Sm content, while oxygen content increased up to amaximum of about 50 at %. For short T_(on) (few ms), oxygen content wasas low as 3 at % (PCD=1000 mA/cm²). In-plane coercivities up to 5.3 kOehave been achieved for as-plated nanoparticles for Sm content of about20 at %.

D. Applications of Magnetic Co—Sm Alloys

In one aspect, the disclosed method and compositions can be used inconnection with high performance nanostructured permanent magnetsincluding high temperature applications in aeronautical and aerospaceapplications. In a further aspect, the disclosed method and compositionscan be used to produce dramatically miniaturized devices includingelectric motors, generators, actuators, alternators, gyros, magneticcouplings, magnetic bearings, centrifuges, hearing aid devices, computerhard drives, camcorders, industrial robots, maglev trains, and magneticimaging systems (MIS).

In a yet further aspect, the disclosed method and compositions can beused to produce thick film (>1 nm) deposition for microelectromechanicalsystems (MEMS) devices.

In a still further aspect, the disclosed method and compositions can beused to produce ultra thin (<100 nm) controlled electrodeposition fornano-electromechanical systems, and nanosize biomedical devices andneuroelectrochemical applications.

E. Aqueous Electrodeposition Compositions

In one aspect, the invention relates to compositions for enhancing theaqueous electrodeposition of rare earth-transition metal alloyscomprising: a water soluble salt of samarium, a water soluble salt ofcobalt, and a comlexant. In a further aspect, the water soluble salt ofsamarium is samarium sulfamate. In a further aspect, the water solublesalt of cobalt is cobalt sulfate or cobalt sulfamate. In a furtheraspect, the composition comprises one or more supporting electrolytes.In a further aspect, the composition further comprises boric acid. Inone aspect, the electrodeposition can be performed onto a conducting(e.g., metal) substrate.

In one aspect, the complexant can be one or more amino acid. The aminoacid can be any amino acid known to those of skill in the art. In afurther aspect, the amino acid is selected from amine carboxylates, forexample, glycine, alanine, and serine,

In a further aspect, the complexant can be one or more hydroxycarboxylicacid. The hydroxycarboxylic acid can be any hydroxycarboxylic acid knownto those of skill in the art. In a further aspect, the hydroxycarboxylicacid is selcted from malic, glycolic and lactic acids, citric, andtartaric acids.

In one aspect, the one or more supporting electrolytes (e.g., conductingsalts) can be any electrolytes known to those of skill in the art. In afurther aspect, the one or more electrolytes are selected from ammoniumsulfamate, ammonium sulfate, ammonium chloride, and mixtures thereof.

In one aspect, the composition can comprise from about 0.25M to about2.0M of the water soluble salt of samarium, from about 0.01M to about0.5M of the water soluble salt of cobalt, from about 0.05M to about 0.5Mof the complexant, and from about 0.1M to about 3M of the supportingelectrolyte. In a further aspect, the composition can comprise 1M of thewater soluble salt of samarium, 0.05M of the water soluble salt ofcobalt, 0.15M of the complexant, and 1M of the supporting electrolyte.

In one aspect, the water soluble salt of samarium is samarium sulfamate.In one aspect, the water soluble salt of cobalt is cobalt sulfate orcobalt sulfamate. In one aspect, the complexant is an amino acid, forexample, glycine. In one aspect, the complexant is a hydroxycarboxylicacid, for example, malic or citric acid. In one aspect, the conductingsalt is ammonium sulfamate. In a further aspect, the water soluble saltof samarium is samarium sulfamate, the water soluble salt of cobalt iscobalt sulfate or cobalt sulfamate, the complexant is glycine, and thesupporting electrolyte is ammonium sulfamate.

It is understood that the disclosed compositions can be used inconnection with the disclosed methods.

F. Electrodeposition Methods

In one aspect, the invention relates to methods for electrodepositing asamarium-cobalt coating onto a conducting (e.g., metal) substrate,comprising placing an aqueous solution containing a water soluble saltof samarium, a water soluble salt of cobalt, one or more supportingelectrolytes, and a comlexant into a plating bath, placing an anode andthe substrate to be coated into the bath and connecting the anode andthe substrate to a power supply, with the substrate acting as thecathode, adjusting the pH of the bath to a suitable operating level, andapplying a direct current through the anode and substrate causing thesamarium and the cobalt to migrate to, and adhere to, the substrate. Inone aspect, the aqueous solution further comprises boric acid.

In one aspect, the method can further comprise an annealing step.

In one aspect, the complexant can be one or more amino acid. The aminoacid can be any amino acid known to those of skill in the art. In afurther aspect, the amino acid is selected from amine carboxylates, forexample, glycine, alanine, and serine,

In a further aspect, the complexant can be one or more hydroxycarboxylicacid. The hydroxycarboxylic acid can be any hydroxycarboxylic acid knownto those of skill in the art. In a further aspect, the hydroxycarboxylicacid is selcted from malic, glycolic and lactic acids, citric, andtartaric acids.

In one aspect, the one or more supporting electrolytes (e.g., conductingsalts) can be any electrolytes known to those of skill in the art. In afurther aspect, the one or more electrolytes are selected from ammoniumsulfamate, ammonium sulfate, ammonium chloride, and mixtures thereof.

In one aspect, the aqueous solution can comprise from about 0.25M toabout 2.0M of the water soluble salt of samarium, from about 0.01M toabout 0.5M of the water soluble salt of cobalt, from about 0.05M toabout 0.5M of the complexant, and from about 0.0001M to about 3M of thesupporting electrolyte. In a further aspect, the aqueous solution cancomprise about 1M of the water soluble salt of samarium, about 0.05M ofthe water soluble salt of cobalt, about 0.15M of the complexant, andabout 1M of the supporting electrolyte.

In one aspect, the water soluble salt of samarium is samarium sulfamate.In one aspect, the water soluble salt of cobalt is cobalt sulfate orcobalt sulfamate. In one aspect, the complexant is an amino acid, forexample, glycine. In one aspect, the complexant is a hydroxycarboxylicacid, for example, malic or citric acid. In one aspect, the supportingelectrolyte is ammonium sulfamate. In a further aspect, the watersoluble salt of samarium is samarium sulfamate, the water soluble saltof cobalt is cobalt sulfate or cobalt sulfamate, the complexant isglycine, and the supporting electrolyte is ammonium sulfamate.

In one aspect, a current density of from about 5 mA/cm² to about 600mA/cm² is applied across the anode and cathode. In various aspects, thecurrent density can be, for example, from about 5 mA/cm² to about 300mA/cm², from about 5 mA/cm² to about 100 mA/cm², from about 5 mA/cm² toabout 50 mA/cm², from about 5 mA/cm² to about 20 mA/cm², from about 10mA/cm² to about 300 mA/cm², from about 10 mA/cm² to about 100 mA/cm²,from about 10 mA/cm² to about 50 mA/cm², from about 10 mA/cm² to about20 mA/cm², from about 0 mA/cm² to about 300 mA/cm², from about 0 mA/cm²to about 100 mA/cm², from about 0 mA/cm² to about 50 mA/cm², or fromabout 0 mA/cm² to about 20 mA/cm². In a further aspect, the DC currentdensity is a DC current density. In a further aspect, the current is analternating current. In a further aspect, the current is a pulsedcurrent. In a further aspect, the current is applied with pulse currentmodifications varying with duty cycle and frequency.

In one aspect, the pH of the solution is from about 3 to about 6. In afurther aspect, the pH of the solution is adjusted to from about 4 toabout 6.5. In a further aspect, the pH of the solution is about 4.

In one aspect, the electrodeposition is conducted at a temperature offrom grater than about 0° C. to less than about 100° C. In a furtheraspect, the electrodeposition is conducted at a temperature of fromabout 20° C. to about 80° C. In a further aspect, the electrodepositionis conducted at a temperature of from about 20° C. to about 60° C. In afurther aspect, the electrodeposition is conducted at a temperature offrom about 20° C. to about 40° C. In a further aspect, the solutiontemperature is from about 25° C. to about 60° C., for example, about 25°C., about 40° C., or about 60° C. In a yet further aspect, theelectrodeposition is conducted at about room temperature.

The electrodeposition can be conducted with stirring. In a furtheraspect, the electrodeposition is conducted without stirring. In afurther aspect, the electrodeposition is conducted with oscillatorystirring. In a further aspect, the electrodeposition is conducted withoscillatory stirring at a rate of from about 40 to about 60 cycles/min,for example, about 48 cycles/min.

It is understood that the disclosed compositions can be used inconnection with the disclosed methods.

Also disclosed are samarium-cobalt coatings produced by the disclosedmethods.

G. Nanostructured Magnetic Coatings

In one aspect, the invention relates to nanostructured magnetic coatingscomprising a magnetic alloy of a rare earth metal and a transitionmetal. In a further aspect, the coatings are electrodeposited. In afurther aspect, the coatings are electrodeposited from aqueous solution.

In one aspect, the rare earth metal is samarium. In one aspect, thetransition metal is cobalt. In a further aspect, the rare earth metal issamarium and transition metal is cobalt. In a further aspect, the alloycomprises SmCo₅ or Sm₂Co₁₇.

In certain aspects, the electrodeposited alloy contains sufficientsamarium content to perform as a precursor to forming magnetic SmCo₅and/or Sm₂Co₁₇.

It is understood that the disclosed nanostructured magnetic coatings canbe produced using the disclosed methods and compositions.

H. Experimental

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how thecompounds, compositions, articles, devices and/or methods claimed hereinare made and evaluated, and are intended to be purely exemplary of theinvention and are not intended to limit the scope of what the inventorsregard as their invention. Efforts have been made to ensure accuracywith respect to numbers (e.g., amounts, temperature, etc.), but someerrors and deviations should be accounted for. Unless indicatedotherwise, parts are parts by weight, temperature is in ° C. or is atambient temperature, and pressure is at or near atmospheric.

1. Aqueous Electrodeposition of Rare Earth Metals and Transition Metals

Rare earth (e.g., samarium) and transition metal (e.g., cobalt) elementscan be electroplated out of an aqueous solution to form bright metalliccoatings on substrates by proper selection of the additives, such ascomplexing agent, solution pH, operating temperature, current density,complexing agent/metal ratio, complexing agent/transition metal ratio,and duty cycle. Particularly suitable complexing agents are glycine,alanine, and serine, which are all amino acids with a single carboxylgroup. With the exception of cysteine, complexing agents evaluated whichwere not effective were amino acids with more than one carboxyl group orwere not amino acids. Cysteine is an amino acid with one carboxyl groupand a thio- group (—SH). The —SH apparently interfered with obtainingthe desired result by causing the formation of hydroxides under theconditions evaluated.

While varying the operating conditions resulted in lesser concentrationsof the desired materials in the films produced, conditions were stillsuitable for preparing RE containing coatings. The preferred complexingagent is glycine but other aminecarboxylates were also found to beeffective. The preferred operating conditions include a current densityof at least 5 mA/cm², room temperature, a pH of 4, and a Co/glycineratio of about 0.3. However, it has been found that addition of NH₄Cl tothe processing bath sharply reduced hydrogen evolution resulting inhigher RE content deposits. Furthermore, while a pH of 4 is preferred,metallic deposits were obtained over a wide pH range including pH lessthan 4 and greater than 7. Stable alkaline plating baths for RE and TMsalts are disclosed.

Plating solutions can be prepared containing various complexing agents,and transition metals (TM) (e.g., Co, Fe, Ni) and rare earth chloridesalts. The solution pH can be adjusted upward with NaOH and lowered withHCl. Electrodeposition can be carried out at room temperature (RT) withDC current in the solutions containing TMCl.sub.2 and La, Ce, Nd and arare earth mixture (MOLYCORP.TM.) referred to below as the REM mixture.Other commercial rare earth mixtures are also suitable. The compositionof the Molycorp™ mixture is given in Table 2.

TABLE 2 Rare Earth Mixture (Molycorp ™) Analysis Equivalent Wt. PercentElement % as oxide % as carbonate Metal Ce 1.0 1.3 0.7 La 45.9 64.4 39.2Nd 12.9 18.0 11.1 Pr 4.8 6.7 3.9 Sm 0.4 0.6 0.3 Gd 0.3 0.4 0.3 Y 0.3 0.50.2 other RE ~0.4 ~0.6 ~0.4 other elements ~0.1 ~0.2 —

Primary test solutions were (A) Bath A—0.12M TMCl₂, 0.5M B(OH)₃, 0.36Mcomplexing agent, 0.3 M RE or REM (B) Bath B—same as Bath A+1M NH₄ Cl.

Solutions were either unstirred or stirred using a magnetic stirrer orby oscillatory stirring (48 cycles/min).

Each solution was used until accumulative exposure of 240-A-min/L atwhich point a new solution was prepared. The solution becomes lesseffective after 240-A-min/L because of consumption of the keyingredients in the rare earth mixture used. Brass or stainless steelpanels were used as substrates. The substrates were mechanically cleanedand then subjected to a chemical treatment including soaking in alkalinecleaning solution for 10 min followed by rinsing with deionized water.Surfaces were then activated just before electrodeposition by immersionin 10% HCl for 30 sec. Soluble Co, Fe, or Ni anodes were used, dependingon the solution, to minimize changes in the metal solution compositionand to avoid known side effects due to insoluble anodes.

A Kraft Dynatronix power supply (model DRP 20-5) was used to providepulse current (PC) waveforms and a PAR potentiostate/galvanostat (model173) was used to provide DC current.

In order to evaluate the efficiency of the electrodeposition of RE-TMmaterials from solutions containing complexing agents, nitric acid wasused to dissolve the deposited films. After evaporating the nitric acidsolution to dryness, the resultant dried RE-TM residue was dissolvedwith deionized water and transferred to a plastic test tube.Hydrofluoric acid was added to separate the rare earths from ferrousmetals by precipitation of rare earths fluorides. The precipitate wasthoroughly washed with deionized water and transferred to a 50milliliter beaker. Boric acid and nitric acid were then added todissolve the precipitated rare earth fluorides. The solution wasevaporated to dryness, resulting in water-soluble rare earth compounds.The dried sample was redissolved with deionized water and transferredinto a 10 milliliter volumetric flask. One milliliter of ammoniumacetate buffer and a complexing agent (alizarin red) were added.Ammonium acetate was used to buffer the solution to pH of 4.7 and thealizarin red was complexed with the rare earth to develop a specificcolor. After dilution to 10 milliliters, a spectrophotometer (λ=530 nm)was used to measure the absorbance. The absorbance obtained was thenused to estimate the amount of rare earth in the deposit.

For plating solutions free from complexing agents, precipitation byoxalic acid was followed by dissolution of the oxalate precipitate withconcentrated hydrocholoric acid, and finally precipitation with ammonia.The final white hydroxide precipitate from the ammoniacal solutionsconfirmed the presence of lanthanons in the deposit.

a. Effects of Complexing Agents

Using Bath A, eleven (11) complexing agents were investigated to studytheir effects on the production of RE-Co deposits and the stability ofsolutions. The solutions were stirred and exposed to current density of20 mA/cm.sup.2 unless. The results are summarized in Table 3.

TABLE 3 Effects of Complexing Agent* Rare Earth Content Additives inDeposit Appearance Glycine (REM) 8.0% Bright metallic Glycine (Ce) 6.3%Grey metallic Glycine (La) 7.5% Black metallic Glycine (Nd) 3.4% Graymetallic Alanine (REM) 3.8% Bright metallic Serine (REM) 5.0% Brightmetallic Aspartic acid (REM) Not analyzed Non-metallic white (RE)hydroxide Glutamic acid (REM) Not analyzed Non-metallic white (RE)hydroxide Malic acid (REM) No RE Grey metallic (pH 8.5) Cysteine (REM)Not analyzed Non-metallic hydroxide Glycolic acid (REM) 0.2-1% Brightmetallic Lactic acid (REM) 0.2-1% Bright metallic EDTA (REM) No deposit*Solutions (Bath A, pH 4) were stirred and electrodeposition was at 20mA/cm²

It was found that the a-amino acids, glycine, alanine and serinestabilized the plating solution at pH 4, resulting in metallic depositscontaining rare earths. The highest RE content in deposited films wasobtained in solutions containing glycine while deposits of lower REcontent were obtained with alaline and serine. All the depositsexhibited bright metallic appearance, which differed from the typicalmatte appearance of cobalt electrodeposits, indicating the effect of therare earth elements. In order to test which element was preferentiallydeposited from the REM, separate runs were performed in the solutionscontaining glycine and Ce(Cl)₃, Nd(Cl)₃ or La(Cl)₃. The presence oflanthanum in the solution gave a black metallic deposit containing 7.5%lanthanum, 3.4% Nd was obtained with NdCl₃ and these Ce(Cl₃) produced agray metallic deposit with a 6.4% Ce in the films. In these cases, the 3RE content of the deposit was lower than that when the RE mixture (8%)was used.

Solutions containing aspartic acid and glutamic acid were not stable andproduced uniform white precipitates which consisted of RE hydroxidesinstead of metal films. Black deposits were obtained from the solutionscontaining cysteine and those cysteine solutions were also not stable.

The solutions containing glycolic acid or lactic acid were cloudy at pH4due to the formation of small amounts of hydroxides. However, brightmetallic deposits containing small amounts of RE were obtained fromfiltered solutions. EDTA formed strong complexes with Co. As a result,no deposits were obtained from the EDTA containing solutions.

In addition to the results shown in Table 3, a Nd—Ni deposit of 6% Ndwas obtained from Bath B using ethylene diamine as a complexing agent.The solution (pH5) was unstirred and deposits were obtained at 15mA/cm².

b. Effect of Direct Current Deposition

To evaluate the effect of current density on resultant deposits,electrodeposition was carried out at room temperature and currentdensities of 5, 10, and 20 mA/cm² for Co-RE, Ni-RE and Fe-RE solutionscontaining glycine at pH4. The solution contained 0.12M (Fe, Ni, Co)Cl₂, 0.5M B(OH)₃, 0.36M glycine and 0.3 RE (La, Ce, Nd), or REM. FIG. 11compares the dependence of the rare earth content (% rare earth) of thedeposited films at different current densities. Generally, thepercentage of rare earth in the film increased with increasing currentdensity. Deposit content of the rare earths were greater in Ni alloys,less in Fe alloys and least in Co alloys. Rare earth deposit contentsare typically greatest from unstirred solutions, a lesser amount fromsolutions mixed by oscillatory stirring and least from more vigorousagitation with a magnetic stirrer. Thus, mass transfer effects can beimportant in the efficacy of RE-TM electrodeposition.

C. Effect of Temperature

Electrodeposition from magnetic stirred Bath A containing CoCl₂ and therare earth mixture (REM) was run at both room temperature and 65° C. toexamine the temperature dependence of Re—Co deposits. It was found thatat the same current density (20 mA/cm²), the rare earth in the depositsat 65° C. was ˜3%, which was less than half the 6.6% obtained at roomtemperature. Thus, the cobalt deposition rate is greatly enhanced andthe RE deposition reduced as temperature is increased. In other words, alower temperature during electrodeposition favors RE deposition.

d. Effect of Complexing Agent to Metal Ratio

The ratio of the glycine concentration to metal concentrations inmagnetic stirred solutions also had a measurable effect on RE-Coelectrodeposition. FIG. 12 shows the effects of glycine/Co solutionratios with CoCl₂ held constant at 0.12M on the deposit RE contentobtained at room temperature with a current density of 20 mA/cm² and apH of 4. There appears to be a plateau or an approach to a maximum indeposited RE content as the glycine/Co ratio approached 1. At glycine/Coratio>1, a sharp decrease in the deposit RE content with increasingratios was observed (FIG. 12).

e. Effect of Co(Cl)₂+Glycine

In this study, the magnetic stirred solution RE concentration wasmaintained constant at 0.3M while the combined concentrations ofCo(Cl)₂+glycine was increased at a constant ratio: 1Co:3glycine. FIG. 13shows increased Co(Cl)₂+glycine concentrations resulted in decreaseddeposit RE content. At a combined total concentrations of 1.5M,practically no RE was deposited indicating the possibleinhibitory-effect of increasing addition agent concentrations. Again,operating conditions were room temperature, pH of 4 and a currentdensity of 20 mA/cm².

The duty cycle for PC electrodeposition is defined ast_(on)/(t_(on)+t_(off)), and the average current density is the peakcurrent density times the duty cycle. Pulsed current deposition of RE-Coalloys was performed at an average current density of 20 mA/cm² withT_(on) at 5 msec. FIG. 14 shows that the deposit RE content was fairlyconstant at ˜4.5±5% at duty cycles from 0.1 to 0.8. In this range, thepeak cathodic current densities ranged from 200 to 25 mA/cm², along withdecreasing off-times of 45 to 1.75 msec, respectively. At duty cyclesgreater than 0.8, approaching DC plating, the deposit RE contentincreased to ˜6.+1% and was similar to that obtained with constant DCcurrent.

As the peak cathodic current density increased, the required longeroff-times (relaxation times) permitted sufficient diffusion of either orboth the Co or RE species into the cathode diffusion layer. However, atany peak cathodic current density greater than DC, the diffusion of theRE was insufficient to provide the necessary replenishment, resulting inlower deposit content, although the bulk solution concentration wasthree times that of cobalt. More Co deposited during the on-timeindicating either fast deposition rates or mass transfer compared to theRE.

For Co—Re deposition, deposit RE content was relatively constant with PCdeposition up to duty cycle of 0.8 and then increased at higher dutycycle. DC electrodeposition gave the highest amount of RE in the films.Temperatures greater than room temperature increased additive to metalratio, and increased cobalt concentration resulted in lower RE in thefilms.

f. Effect of Solution Ph and NH₄Cl

The solution pH can be important to the electrodeposition process. ThepH can affect the onset of the hydrogen evolution reaction, thecomposition of the deposits, the current efficiencies and the stabilityof the solution. Addition of NH₄Cl to Bath A was an effort to lessen therate of hydrogen evolution. FIG. 15 illustrates the interdependence ofcurrent density with solution pH on the composition of deposits obtainedfrom TM-Nd-glycine solutions. In general, the deposit Nd contentincreased fairly linearly with increasing current density and increasingsolution pH in the range of 5-40 mA/cm² and pH4-5.4, respectively, theexception being Nd—Ni deposits which exhibited a maximum deposit contentat 10 mA/cm² and solution pH of 4.8.

It was observed that the presence of NH₄Cl significantly decreasedhydrogen evolution during electrodeposition of RE-TM alloys. As a resultthe pH range to obtain metallic deposits was increased. For example, 29%Ce in Ce—Ni deposits were obtained with glycine @ pH2.7 and 15 mA/sq.cm(Bath B) and 23% Nd was obtained in Nd—Ni deposits with alanine)@pH7 and20 mA/sq.cm (Bath B). Furthermore, deposit RE content was generallyhigher in solutions containing NH₄Cl. For example, for Ce—Ni deposits at5 and 20 mA/cm² with oscillatory stirring (Bath B), Ce contents were10.5% and 22.5%, respectively. In comparison 8.2% and 16.2% wereobtained from Bath A.

g. Mass Transfer Effects

The degree of solution agitation during electrodeposition of RE-TMalloys can have an effect on the RE content of the deposits. FIG. 16shows that the Ce content in Ce—Ni deposits was less from oscillatorystirred solutions (48 cycles/min) compared to unstirred solutions.Further, RE deposit contents were even lower from solutions agitatedmore vigorously using a magnetic stirrer. On the other hand, visualinspection of the deposits indicates that solution agitation improvedthe quality (appearance) of the deposits. For the electrodeposition ofbright metallic or ferrous metal-RE alloys, the most effectivecomplexing agents appear to include glycine, alanine and serine. Thesecomplexing agents are amino acids with a specific chemical structure,namely a single carboxyl group and thus differ chemically from the othersampled complexing agents which were not found to be suitable.Therefore, it would appear that other amino acids with single carboxylgroups would be suitable compounds to create the same result undersimilar operating conditions and solution compositions. Other types ofcomplexing agents investigated were either not as effective orineffective, usually resulted in precipitation of hydroxide in thesolution and/or in the deposited films or prevented deposition of the REor resulted in unacceptable appearing films.

2. Hull Cell Studies

Co—Sm permanent magnets, such as Sm₂Co₁₇ and SmCo₅, require 10.53 and16.67 at % Sm content, respectively. To satisfy the compositionrequirements of Co—Sm magnets, the alloys produced by electrodepositionmust contain enough Sm content. Therefore, high Sm content Co—Sm alloyselectrodeposited from aqueous solution is the initial goal of thisresearch.

An electrodeposition process can be operated successfully only when thekey parameters are properly controlled. These are components andcompositions of plating baths (e.g. metal ions, supporting electrolytesand additives) and operating conditions (e.g. current density (CD),solution temperature, pH, fluid dynamics and current waveforms). Toobtain high Sm deposit content, these parameters need to be studiedcarefully.

The Hull cell is an effective screening device often used byelectroplaters to solve problems of the electroplating process. The Hullcell has been recognized as a powerful tool to study the approximatedeposit properties. Generally, the Hull cell provides informationregarding the deposit characteristics over a wide range of CDs andmultiple experimental results in a single experiment. For its highefficiency, Hull cell technology was chosen to determine the dependenceof Sm deposit content on deposit parameters and coupling between depositparameters in the electrodeposition of Co—Sm alloys. Although the resultby the Hull cell is less accurate and more limited than by parallelelectrodes, it still provides a good approximation to the trends in Smdeposit content by varying the electrodeposition parameters in theinitial investigations of the electrodeposition of Co—Sm alloys.

FIG. 17 shows the flowchart of a Hull cell experiment which mainlyincludes four parts: pretreatment of cathode, DC or PCelectrodeposition, post-treatment of specimen and characterization.Fundamentals, definitions, experimental setup, design of Hull cellstudy, pretreatment and post-treatment, and characterization andanalysis of the specimens will be described in the following discussion.

a. Fundamentals of the Hull Cell

The Hull cell, developed by R. O. Hull [R. O. Hull, U.S. Pat. No.2,149,344 (1939)], is a miniature trapezoidal plating cell (267 mL vol)which provides a current density (CD) range on the cathode test panel,depending on the applied current. FIG. 18 shows Hull cell cathode testpanel at the right end (point b), having the longest cathode-anodedistance (D_(b)), resulting in the lowest CD; the CD continuouslyincreases as the current path along the cathode decreases and reaches amaximum at point a, the shortest cathode-anode distance (D_(a)).

Thus, it is universally used as an economical screening device toevaluate the effects of solution compositions and applied operatingconditions on the deposit appearance, composition and crystal structureas a result of incremental CDs on a single cathode surface, especiallyfor initial investigations of alloy electrodeposition. Further, depositson selected portions of the test panel can be analyzed by energydispersive spectroscopy (EDS) and X-ray diffraction (XRD) to provideadditional information regarding compositions and crystal structures.The current density at which the deposit no longer has a metallicappearance, referred to as “burnt” by practicing electroplaters, wasdefined as the maximum current density (CD_(max)) for a particularplating system.

To minimize solution concentration and temperature gradients duringelectrodeposition, the Hull cell was equipped with a motorized slidemechanism with an attached paddle located alongside the cathodeproviding a reciprocal horizontal motion (agitation) with a sweep rateof 80 cycles/min, regulated by a variable resistor.

Hull developed an equation describing the CD distribution on the testpanel for a typical 267 mL Hull cell:

CD=I(27.7−48.7 log L)A/ft² (ASF)   (Equation 6)

where I is the applied current in amperes, and L is the position on thetest panel in inches from the low CD end (point b). This equation wasderived basing on the standard 10×5 cm (area=50 cm²) Hull cell panel.The design of the Hull cell allows us to obtain deposits at differentCDs on a single substrate. In other words, it saves a lot of time byproviding a spectrum (Hull cell pattern) of a deposit obtained atcontinuous changing CD along its length on a single panel. The depositscan then be analyzed to determine properties at a particular CD.

However, the design of the Hull cell is based on primary current densitydistribution neglecting the secondary density distribution [L. J.Durney, Electroplating Engineering Handbook (4th edition), Van NostrandReinhold Company Inc., Taiwan, (1984), pp. 461-473] due to the depletionof metal ions at cathode surface during the electrodeposition. Theapparent CDs on the test panel, as calculated with Equation 6, onlyprovide an approximation of the “true” CDs. Therefore, the analysis inHull cell only shows the trends rather than the precise values ofdeposit properties changed by electrodeposition parameters. Only Smdeposit contents (by EDS) and crystal structures (by XRD) were analyzedin the Hull cell test. In addition, analysis of the deposit at CD_(max)is difficult to determine because cutting a piece of specimen atCD_(max) non-metallic deposits at CDs slightly higher than CD_(max) wereincluded. Compared to the result by parallel electrodes depositions, theHull cell result is less accurate and more limited. Although the Hullcell has these drawbacks, it is still an efficient device providing agood approximation of trends for the preliminary investigation of theelectrodeposition of Co—Sm alloys.

b. Definitions and Parameters

DC&PC electrodeposition: Metallic deposit is defined as a deposit with avisual metallic-appearance, Sm content (at %) is defined as the atomicpercentage of Sm in deposited total metals, Sm content

$\left( {{at}\mspace{14mu} \%} \right) = {{\frac{Sm}{{total}\mspace{14mu} {metals}}\left( {{at}\mspace{14mu} \%} \right)} = {\frac{Sm}{{Sm} + {Co}}\left( {{at}\mspace{14mu} \%} \right)}}$

DC electrodeposition: CD is the current density defined as current perunit deposit area, CD_(max), is defined as the highest CD to obtainmetallic-appearing deposits.

PC electrodeposition: PCD is peak current density defined as the maximumCD in one complete pulse cycle, PCD_(max) is defined as the highest PCDto obtain metallic appearing deposits, T_(on), is the time duration ofthe on-current in one complete pulse cycle, T_(off) is the time durationof the off-current in one complete pulse cycle, Period is the timeduration for one complete cycle, period=T_(total)=T_(on)+T_(off),Frequency (f) is defined as the number of complete cycles per second,

$f = {\frac{1}{period} = \frac{1}{T_{on} + T_{off}}}$

Duty cycle (γ) is defined as the ratio of T_(on) to period,

$\gamma = {\frac{T_{on}}{T_{on} + T_{off}} = {T_{on}f}}$

c. Experimental Setup and Design

The setup for Hull cell electrodeposition is shown in FIG. 20. A KraftDynatronix power generator (model DRP 20-5-10) served as power source tosupply current needed for DC and PC electrodeposition, a coulometer tomeasure the total charge passed, and an oscilloscope to monitor thewaveform during pulse current electrodeposition. Masked brass panels(10×5 cm) with exposed 15 cm² (10×1.5 cm) deposit area for DC and with7.5 cm² (10×0.75 cm) for PC electrodeposition served as cathodes and aplatinum sheet (5×5 cm) was used as the anode.

The reduction of deposit area from 50 cm² (whole brass panel) to 15 cm²(DC) or 7.5 cm² (PC) increased the CD range for the parametric studies.Therefore, equation 1 was modified by using 15 cm² (or 7.5 cm²) depositarea:

CD=I(85.8.−150.8 log L), mA/cm² (4.5 A/15 cm²)   (Equation 2)

CD=1(171.6.−301.610 log L), mA/cm²(4.5 A/7.5 cm²)   (Equation 3)

where 1 is the total applied current in amperes, and L is the positionon the test panel in inches from the low CD end (right end).

The deposits were obtained in a 267 mL Hull cell filled with the platingbaths as shown in Table 4.

TABLE 4 Plating baths used in Hull cell studies Bath # Sm sulfamate Cosulfate Glycine NH₄ Sulfamate pH 1 1 M 0.05 M 0.15 M 5.7 2 1 M 5.8 3 1 M0.15 M 5.7 4 0.05 M 5.6 5 0.05 M 0.15 M 4.5 6 1 M 0.05 M 5.9 7 1 M 0.05M   3 M 4.0 8 1 M 0.05 M 0.15 M 1 M 5.9 *The pH values of the platingbaths were measured at 25° C.

Bath 1 was used to study the effect of CD and temperature; baths 2 and 3were used to study the effect of glycine on the formation of Sm oxideand hydroxide; baths 4 and 5 were used to study the effects of glycineon the electrodeposition of Co; baths 1, 6 and 7 were used to study theeffect of the glycine concentration on the codeposition of Sm and Co;baths 1 and 8 were used to study the effect of ammonium sulfamate, asthe supporting electrolyte.

Unless otherwise noted, the total charge passed was 100 coulombs for DCand 50 coulombs for PC electrodeposition to provide deposits thickenough to be analyzed. The deposit area was 15 cm² for DC and 7.5 cm²for PC electrodeposition. The applied charge density remained constantas 6.67 C/cm² for both DC and PC. The applied current was 4.5 A for DC(25 and 60° C.) and for PC at 25° C. and 7A at 60° C. providing a widerange of CDs. Solutions were not agitated during electrodeposition.

(1) Pretreatment and Post-Treatment

Before electrodeposition, the brass panels were mechanically cleanedwith a brush, soaked in 0.1M NaOH for 10 min., rinsed in deionizedwater, immersed in 10% HCl for 30 seconds and then rinsed with deionizedwater.

After the Co—Sm alloy was deposited for 100 coulombs in DC or 50coulombs in PC, deposits were removed from the plating solution, rinsedwith deionized water, and then dried with nitrogen gas. Disk-shapedspecimens of diameter of 3.2 mm (specimen area=8.04 mm²) weredie-punched out from deposits for analysis.

(2) Characterization and Analysis

The main purpose of the Hull cell study is to determine the trend in Smdeposit content by varying the electrodeposition parameters; the Smdeposit content was determined by energy dispersive x-ray spectroscopy(EDS) by a Kevex detector within a Cambridge scanning electronmicroscopy (SEM) (model Stereoscan 250). A PANalytical X-ray diffraction(XRD) (model X'Pert Pro) was used to examine crystal structures ofdeposits by {tilde over (Θ)}2Θ scan method. Unless otherwise noted, theexperimental data presented are restricted to metallic-appearancedeposits.

(3) Energy Dispersive X-Ray Spectrometer (EDS)

EDS measures the energy and intensity distribution of X-rays generatedby the bombardment of electron beam on the specimen. The composition ofthe specimen can be obtained by comparing the peak intensities of Co(K_(α1), 6.93 ev) and Sm (L_(α1), 5.62 ev) to the intensities of theinternal standard of pure Co and Sm, respectively, to get the k′-ratios

$\left( {k^{\prime} = \frac{I_{{specimen}\mspace{14mu} i}}{I_{{pure}\mspace{14mu} {element}\mspace{14mu} i}}} \right)$

then calibrated by ZKF method (a matrix correction technology) to getthe k-ratios of Co and Sm. K-ratios, which are proportional to theweight percent of elements in the specimens, were used to obtain theweight and atomic percent of Co and Sm. An example of energy dispersivespectrum of an electrodeposited Co—Sm alloy is given in FIG. 21 and theanalysis result is shown in Table 5. The elemental composition in adefined scan area can be easily determined to a high degree of precision(−0.1 wt. %).

TABLE 5 Compositional analysis results of an electrodeposited Co—Smalloy Element Peak Peak Intensity (cps) K-Ratio Weight % Atomic % Co Kα₁1793.4 0.8558 85.77 93.89 Sm Lα₁ 149.2 0.1442 14.23 6.11

(4) X-Ray Diffraction (XRD)

XRD [L. V. Azaroff, Elements of X-ray crystallography, McGraw-Hill,N.Y., (1968)] is a technique in crystallography which can be used todetermine the crystal structures of the specimen by characterizing itsdiffraction pattern with Bragg's law. The shape and size of the unitcell determines the angular position (2Θ) of the diffraction lines; thearrangement of the atoms within the unit cell determines the relativeintensities of the lines. Information regarding states of Co—Sm alloys(e.g. crystalline, non-crystalline, intermetallic compound),non-metallic compounds (e.g., oxide and hydroxide), and preferorientation (PO) of deposits can be examined by diffraction peaks. Thesecharacteristics of electrodeposited Co—Sm alloys controlled byelectrodeposition parameters are very useful to study magnetic, electricand mechanical properties of deposits.

The grain size of the crystallites in out-of-plane direction(perpendicular to film plane) can be estimated from the measured widthof their diffraction peaks by Scherrer's formula [B. D. Cullity and S.R. Stock, Elements of X-ray diffraction (3rd edition), Prentice Hall,N.J., (2001), p170]:

$t = \frac{0.9\mspace{11mu} \lambda}{B\; {{Cos}\left( \theta_{B} \right)}}$

where λ is the wavelength of X-ray used to obtain the diffractionpattern; B is the full-width at half maximum (FWHM), and Θ_(B) is theBragg's angle of the diffraction peak.

(5) Effect of Applied Charge, Current and Deposit Area

As indicated, various applied charges (100 C/15 cm² for DC and 50 C/7.5cm² for PC) and currents (4.5 A/15 cm² for DC (25 and 60° C.), 4.5 A/7.5cm² for PC at 25° C. and 7 A/7.5 cm² for PC at 60° C.) were applied toobtain Hull cell patterns. To confirm the results of CD_(max) (orPCD_(max)) obtained at different operating conditions can be compared,some pre-tests were done as follows.

Effect of different applied currents: The purpose of this test was toevaluate the consistency of PCD_(max) at various applied currents. FIG.22 shows the Hull cell patterns obtained at 60° C. from bath 1 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine) by PC electrodeposition ofapplied current of 4.5 and 7 A. The PCD_(max,) of 4.5 A was about 990mA/cm² which was close to the PCD_(max) of 7 A (about 1000 mA/cm²). Itwas concluded that PCD_(max) at different applied currents varied littleand the Hull cell patterns obtained at different applied currents (4.5and 7 A) can be compared. On the other hand, the application of current7 A provided a wider PCD range on Hull cell patterns obtaining moreinformation of the oxide/hydroxide region (FIG. 22( b) compared to 4.5 A(FIG. 22( a)). Therefore, a current of 7 A was applied in PC at 60° C.instead of 4.5 A for a wider PCD range. PCD_(max) remained unchanged,and Hull cell patterns obtained at the current of 4.5 and 7 A can becompared.

Effect of different applied charges: The purpose of this test was tocheck the consistency of PCD_(max) at a fixed charge density. FIG. 23shows the Hull cell patterns by PC electrodeposition at 25° C. from bath1 for applied charge/deposit area of 100 C/15 cm² and 50 C/7.5 cm²(charge density was fixed at 6.67 C/cm²). The PCD_(max) of 100 C/15 cm²was about 190 mA/cm² which was close to the PCD_(max) of 50 C/7.5 cm²(about 200 mA/cm²). It was concluded that as long as the charge densitywas constant (charge/deposit area=6.67 C/cm²), PCD_(max) varied little.Therefore, in PC electrodeposition, the PCD_(max) of Hull cell patternsobtained at 100 C/15 cm² and 50/7.5 cm² can be compared.

(6) Results and Discussions of DC Electrodeposition

Effect of current density and solution temperature: Bath 1 (1M Smsulfamate, 0.05M Co sulfate, 0.15M glycine) was used to study theeffects of current density and solution temperature on theelectrodeposited Co—Sm alloys. The experimental conditions are shown inTable 6, and their Hull cell patterns in FIG. 24.

TABLE 6 The effects of current density and solution temperature[Sm(NH₂SO₃)₃] [CoSO₄] T CD_(max) EXP # Bath (M) (M) [Glycine] (M) pH (°C.) (mA/cm²) 3 1 1.00 0.05 0.15 5.7 25 50 6 60 750 45 80 850 * Totalcharge = 100 C, applied current = 4.5 A, substrate area = 15 cm², pH =5.7, no agitation.

Deposits obtained from bath 1 at 25° C., for example, showedmetallic-appearing for CD below 50 mA/cm², burnt between 50 and 100mA/cm², and white powder at CD above 100 mA/cm² (FIG. 24( a)). Tocharacterize these regions, XRD was used to study their phasecompositions. From the result of XRD patterns of deposit #3 (FIG. 25),the metallic region was non-crystalline and contained a weak diffractionpeak of Sm(OH)₃ (FIG. 25( a)). The burnt region exhibited not onlySm(OH)₃ but also Co(OH)₂ and SmO peaks (FIG. 25( b)). The non-metallicwhite powder region (FIG. 25( c)) contained Sm(OH)₃, Co(OH)₂ andmixtures of Sm and Co oxides.

Generally, metallic deposits could be obtained only below critical CD;at higher CDs, non-metallic appearing deposits containing hydroxides andoxides were obtained. This critical CD was defined as the maximumcurrent density (CD_(max)) to obtain metallic deposits. It was observedthat CD_(max) increased with increasing solution temperature (Table 6and FIG. 24). For example, CD_(max) increased from 50 to 850 mA/cm² byincreased solution temperature from 25 to 80° C. Higher CD resulted inhigher Sm deposit content as shown in FIG. 26. Therefore, high Smdeposit content of 25 at % can be obtained from bath 1 at 60° C. and 650mA/cm² exceeding the composition requirement of 16.67 at % for SmCo₅.(Note: The deposit obtained at 60° C. and 750 mA/cm² (CD_(max)) shouldhave higher Sm deposit content than at 650 A/cm². However, it wasdifficult to measure the Sm content at CD_(max) because it was too closeto the non-metallic region.)

(7) Effect of Fluid Dynamics

Bath 1 was used to study the effect of fluid dynamics onelectrodeposition of Co—Sm alloy. Solution agitation was achieved by aperiodic reciprocal movement of the paddle along the Hull cell panelcontrolled by a motor (FIG. 27).

The experimental conditions are provided in Table 7, and the Hull cellpatterns of the deposits are shown in FIG. 28. Solution agitation didn'tsignificantly affect CD_(max) (FIG. 28) and Sm deposit content (FIG. 29)at either 25 or 60° C. To study mass transfer effect in theelectrodeposition of Co—Sm alloy, a more controlled method, RDE(rotating disk electrode), was used, and the results are discussed in DCelectrodeposition studies.

TABLE 7 The effect of fluid dynamics [Sm(NH₂SO₃)₃] [CoSO₄] [Glycine]Agitation T CD_(max) EXP # Bath (M) (M) (M) (cycles/min) (° C.) (mA/cm²)3 1 1.00 0.05 0.15 0 25 50 9 80 50 6 0 60 750 12 80 750 *Total applycharge = 100 C, applied current = 4.5 A, substrate area = 15 cm² (10 cm× 1.5 cm), pH = 5.7.

(8) Effect of Glycine on the Electrodeposition of Sm and Co

Like other RE metals, metallic Sm has not been deposited from aqueoussolution, generally attributed to its very negative reduction potential[W. M. Latimer, The Oxidation States of the Elements and TheirPotentials in Aqueous Solution, Prentice-Hall, N.Y., pp. 286-295 (1952)](E°<−2.3V_(SHE)). Compared to Sm, water has a much less negativereduction potential [W. M. Latimer, The Oxidation States of the Elementsand Their Potentials in Aqueous Solution, Prentice-Hall, N.Y., pp. 29-37(1952)] (2H₂O+4e⁻→2OH⁻+H₂, E≧−0.826V). Typically, hydroxyl ionsgenerated by hydrogen evolution react with Sm ions to form hydroxides.However, metallic codeposits of Co—Sm have been obtained from aqueoussolutions containing glycine and its derivatives [L. Chen, M. Schwartz,and K. Nobe, in Electrodeposited Thin Films, M. Paunovic; M. Schwartz,F. He, N. Myung, and K. Nobe, in Magnetic Materials, Processes, andDevices V. Applications to Storage and Microelectromechanical Systems(MEMS), L. T. Romankiw, S. Krongelb, and C. H. Ahn, Editors, PV 98029,p. 646, The Electrochemical Society Proceedings Series, Pennington, N.J.(1999); N. V. Myung, M. Schwartz, and K. Nobe, in Fundamental Aspects ofElectrochemical Deposition and Dissolution, M. Matlosz, D. Landolt, R.Aogaki, Y. Sato, and J . B. Talbot, Editors, PV 99-33, p. 263, TheElectrochemical Society Proceedings Series, Pennington, N.J. (1999).; M.Schwartz, N. V. Myung, and K. Nobe, J. Electrochem. Soc., 151, C468,(2004).]. Therefore, it is of interest to study the effect of glycine onthe codeposition of Co—Sm alloys.

Various solutions were used to study the effect of glycine on theformation of samarium oxide and hydroxide (bath 2 and 3), theelectrodeposition of cobalt (bath 4 and 5), and the codeposition ofsamarium and cobalt (bath 1, 6 and 7).

(9) Formation of Sm Oxide and Hydroxide

Bath 2 (1M Sm sulfamate) and bath 3 (1M Sm sulfamate, 0.15M glycine)shown in Table 8 were used to study the effect of glycine on theformation of Sm oxide/hydroxide at 25 and 60° C. FIG. 30 shows theresults of the Hull cell patterns.

TABLE 8 The effect of glycine on formation of Sm oxide/hydroxide EXP[CoSO₄] [Glycine] T # Bath [Sm(NH₂SO₃)₃] (M) (M) (M) pH (° C.) 41 2 1.000 0 5.8 25 42 60 43 3 0.15 5.7 25 44 60 *Total charge = 100 C, appliedcurrent = 4.5 A, substrate area = 15 cm², no agitation.

Addition of glycine to Sm sulfamate solution did not result in metallicSm deposits. However, it seems to play a role to stabilize Sm ions insolution and reduce the formation of hydroxides and oxides in deposits.It was noted that a mixture of Sm hydroxide/oxide was formed when CDreached a critical point; addition of glycine to the electrolytedecreased the formation of hydroxides and oxides by extending thiscritical CD. At 25° C., for example, the critical CD increased from 60to 150 mA/cm² by addition of 0.15M glycine to 1M Sm sulfamate (FIGS. 30(a) & (b)). Similar results were found at 60° C. (FIGS. 30( c) & (d)).For solutions with glycine present, higher CDs were needed to form Smhydroxide. It has been reported that glycine derivatives complex Sm ions[J. Torres, C. Kremer, E. Kremer, H. Pardo, L. Suescun, A. Mombru, S.Dominguez and A. Mederos , Inorg. Chinn. Acta, 355, 442 (2003); J.Torres, C. Kremer, E. Kremer, H. Pardo, L. Suescun, A. Mombru, S.Dominguez and A. Mederos , J. Alloy Comp., 323-324, 119 (2001)] andprevent the precipitation of Sm(OH)₃ [F. Medrano, A. Calderon and A. K.Yatsimirsky, Chem. Commmun., 1968, (2003)] by complexation of glycineand Sm ions reducing reaction of Sm³⁺ and hydroxyl ions.

It was also observed that increasing solution temperature also depressedformation of Sin hydroxide and oxide without (FIGS. 30( a) & (c)) orwith glycine (FIGS. 30( b) & (d)) by extending the critical CD. Inbrief, it was found that addition of glycine and an increase in solutiontemperature depressed the formation of Sm oxide and hydroxide in thedeposits.

(10) Electrodeposition of CO

Bath 4 (0.05M Co sulfate) and bath 5 (0.05M Co sulfate, 0.15M glycine)shown in Table 9 were used to study the effect of glycine on theelectrodeposition of Co at 25 and 60° C. FIG. 31 shows the Hull cellpatterns. Adding glycine (bath 5) effectively increased CD_(max),especially at 60° C. CD_(max) increased from 90 to 500 mA/cm² at 60° C.by the addition of 0.15M glycine into bath 4. It has been reported thatthe Co-glycine complex can inhibit the formation of Co(OH)₂.[C. F.Diven,F. Wang, A. M. Abukhdeir, W. Salah, B. T. Layden, C. F. Geraldes,and D. M. Freitas, Inorg. Chem., 42, 2774, (2003)] Therefore, additionof glycine appears to prevent the formation of Co(OH)₂, and extended themetallic deposit region to higher CDs.

TABLE 9 The effect of glycine on electrodeposition of Co [Sm(NH₂SO₃)₃][Glycine] CD_(max) EXP # Bath (M) [CoSO₄] (M) (M) pH T (° C.) (mA/cm²)151 4 0 0.05 0 5.6 25 30 152 60 90 153 5 0.15 4.5 25 110 154 60 500*Total charge = 100 C, applied current = 4.5 A, substrate area = 15 cm²(10 cm × 1.5 cm), no agitation.

An increase in solution temperature also increased CD_(max). Depositsobtained from bath 5 increased CDma, from 110 to 500 mA/cm² byincreasing solution temperature from 25 to 60° C. In summary, additionof glycine and increase of solution temperatures resulted in higherCD_(max).

(11) Electrodeposition of Co—Sm Alloys

As discussed in the previous sections, glycine can form complexesindividually with both Sm and Co ions. Sm³⁺ complexed with glycine cannot be electrodeposited to Sm (FIG. 30). Previous work [M. Schwartz, F.He, N. Myung, and K. Nobe, in Magnetic Materials, Processes, and DevicesV. Applications to Storage and Microelectromechanical Systems (MEMS), L.T. Romankiw, S. Krongelb, and C. H. Ahn, Editors, PV 98029, p. 646, TheElectrochemical Society Proceedings Series, Pennington, N.J. (1999)] hasshown that Co—Sm alloys can be electrodeposited from aqueous solutionscontaining Sm³⁺, Co and glycine (or other appropriate complexers).Electrodeposition of Co—Sm alloys have been studied at 25 and 60° C. inthe absence and the presence of glycine at two concentrations; Bath 6(1M Sm sulfamate, 0.05M Co sulfate), bath 1 (1M Sm sulfamate, 0.05M Cosulfate, 0.15M glycine) and bath 7 (1M Sm sulfamate, 0.05M Co sulfate,3M glycine) were selected, as shown in Table 10. The Hull cell patternsand Sm content of deposits from these three baths are shown in FIG. 32(for 25 and 60° C.) and FIG. 33 (for 60° C. only), respectively. In theabsence of glycine, deposits had metallic appearance but containedconsiderable hydroxides/oxides.

TABLE 10 The effect of glycine on electrodeposition of Co—Sm alloys at25 and 60° C. [CoSO₄] [Glycine] T CD_(max) EXP # Bath [Sm(NH₂SO₃)₃] (M)(M) (M) pH (° C.) (mA/cm²) 15 6 1.00 0.05 0 5.8 25 20 3 1 0.15 5.7 50 257 3.00 4.0 40 22 6 1.00 0.05 0 5.8 60 150 6 1 0.15 5.7 750 31 7 3.00 4.0650 *Total charge = 100 C, applied current = 4.5 A, substrate area = 15cm², no agitation.

The addition of glycine extended the metallic deposit region byincreasing CD_(max). CD_(max) from 0 to 3M (FIG. 32) increased, reacheda maximum, and then decreased with increased glycine concentration. At60° C., for example, the CD_(max) increased from 150 mA/cm² (noglycine), reached a maximum of 750 mA/cm² (0.15M glycine), then slightlydecreased to 650 mA/cm² (3M glycine).

Differing from other metallic deposits observed in previous sections, itwas noted that the surfaces of “metallic” deposits from bath 6 (noglycine) at 25 and 60° C. were covered by a thin gray coating. Thesefilms contained oxides and hydroxides of Co and Sm (FIGS. 34( b) & (c)).On the other hand, oxides/hydroxides were not found in the metallicdeposit obtained from the bath 1 (with 0.15M glycine) at 60° C. (650mA/cm²) (FIG. 34( a)) and only a weak (11.0) peak was observed at 25° C.(50 mA/cm²) (FIG. 34( b)). The addition of glycine apparently suppressedformation of oxides and hydroxides. In the absence of glycine, bath 6became unstable and white precipitates formed after 24 hours. Additionof glycine apparently stabilized the solution preventing the formationof hydroxides in the solution.

It is interesting that the Sm oxides included SmO in the depositsobtained from solutions without glycine (FIGS. 34( b) & (c)) indicatingthat Sm(II) may form during electrodeposition. Reduction potential ofSm²⁺ to Sm is much more negative, E°=−2.67 V_(SHE), than Sm³⁺/Sm²⁺(E°=−1.55V_(SHE)).W. M. Latimer, The Oxidation States of the Elementsand Their Potentials in Aqueous Solution, Prentice-Hall, N.Y., pp.286-295 (1952) Glycine forms complexes with Co and Sm ions enablingco-deposition of Co—Sm alloys. By addition of 0.15M glycine (bath 1), arelatively high Sm deposit content of 25 at % was obtained at 650 mA/cm²and 60° C.

By addition of excess glycine (3M glycine, 60° C. bath 7), CD_(max)decreased (FIG. 32( f)) and Sm deposit content decreased (FIG. 33). At60° C. and 400 mA/cm², for example, the Sm content drops substantiallyfrom 14.7 to 2.9 at % as the concentration of glycine increased from0.15 to 3M. Excess glycine may complex virtually all of the Co²⁺ andadditional Sm³⁺ resulting in the formation of mononuclear complexes,Co(gly)⁻ ₃ and Sm(gly)⁻ ₃, at the expense of forming the heterodinuclearcomplexes required for the codeposition of Co—Sm alloys as proposedpreviously.[N. V. Myung, M. Schwartz, and K. Nobe, in FundamentalAspects of Electrochemical Deposition and Dissolution, M. Matlosz, D.Landolt, R. Aogaki, Y. Sato, and J. B. Talbot, Editors, PV 99-33, p.263, The Electrochemical Society Proceedings Series, Pennington, N.J.(1999).]

(12) Effect of Ammonium Sulfamate Concentration

Ammonium sulfamate as supporting electrolyte in the plating bath hasbeen used in a previous study [M. Schwartz, F. He, N. Myung, and K.Nobe, in Magnetic Materials, Processes, and Devices V. Applications toStorage and Microelectromechanical Systems (MEMS), L. T. Romankiw, S.Krongelb, and C. H. Ahn, Editors, PV 98029, p. 646, The ElectrochemicalSociety Proceedings Series, Pennington, N.J. (1999)]. However, theeffect with/without ammonium sulfamate on deposit properties (especiallySm content) has not been carefully studied yet. Bath 1 (1M Sm sulfamate,0.05M Co sulfate, 0.15M glycine) and bath 8 (1M Sm sulfamate, 0.05M Cosulfate, 0.15M glycine, 1M NH₄ sulfamate) were used to study the effectof ammonium sulfamate as shown in Table 11. The Hull cell patterns ofthese deposits are given in FIG. 35.

TABLE 11 The effect of ammonium sulfamate [Sm(NH₂SO₃)₃] [CoSO₄][Glycine] [NH₄(NH₂SO₃] T CD_(max) EXP # Bath (M) (M) (M) (M) (° C.)(mA/cm²) 3 1 1.00 0.05 0.15 0 25 50 6 60 750 34 8 1 25 240 40 60 900*Total charge = 100 C, applied current = 4.5 A, substrate area = 15 cm²(10 cm × 1.5 cm), no agitation.

The presence of 1M ammonium sulfamate resulted in increased CD_(max) at25 and 60° C. For example, at 25° C., the CD_(max) increased from 50 to240 mA/cm² by addition of 1M ammonium sulfamate (FIGS. 35( a) and (c)),but Sm content decreased, especially at 60° C. and higher CDs (FIG. 36).At 60° C., the highest Sm deposit content dramatically dropped from 25to 12 at % (at 650 mA/cm²) by addition of 1M ammonium sulfamate.

(13) Results and Discussion of Pulse Current (PC) Electrodeposition

Effect of peak current density (PCD) and solution temperature: Sincemetallic deposits obtained at higher CD have higher Sm contents, PCelectrodeposition, which enables higher PCD than DC, was used toincrease the Sm deposit content. Bath 1 was used to study the effects ofPCD and solution temperature on PC electrodeposition. Experimentalconditions are given in Table 12, and Hull cell patterns of deposits areshown in FIG. 37.

TABLE 12 The Effect of Peak Current Density T_(on) T_(off) FrequencyPCD_(max.)(or CD_(max)) EXP # Bath (ms) (ms) Duty Cycle (Hz) T (° C.)(mA/cm²) 52 1 10 90 0.1 10 25 200 49 0.05 0.45 2k 1160 56 10 90 10 601000 53 0.05 0.45 2k 2400 3 1 DC 25 50 6 60 750 *In PC, total charge =50 C, substrate area = 7.5 cm² (10 cm × 0.75 cm); at 25° C., appliedcurrent = 4.5 A, at 60° C., applied current = 7 A. In DC, total charge =100 C, substrate area = 15 cm² (10 cm × 1.5 cm), applied current = 4.5A. Both DC and PC were no agitation

It was observed that PC electrodeposition has a larger maximum peakcurrent density (PCD_(max)) than DC (FIG. 37); for example, at 25° C.,the CD_(max) for DC was 50 mA/cm² and the PCD_(max) for T_(on)=0.05 ms(duty cycle=0.1) was 1160 mA/cm². As DC, the PCD_(max) increased withincreased solution temperature. For instance, for deposits obtained frombath 1 at T_(on)=0.05 ms (duty cycle=0.1), PCD_(max) increased from 1160to 2400 mA/cm² by raising the solution temperature from 25 to 60° C.

At 25° C., because PC was able to obtain metallic deposits at higher PCDthan DC, the highest Sm deposit content achieved by PC was greater thanDC (FIG. 38). PC electrodeposition (T_(on)=0.05 ms, duty cycle=0.1)resulted in a maximum Sm content of 19 at % at 580 mA/cm² and 25° C. Atthe same temperature (25° C.) DC electrodeposition had a maximum Smdeposit content of 5 at % at 25 mA/cm².

On the other hand, at higher solution temperature (60° C.) PC did notresult in a higher maximum Sm deposit content than DC electrodeposition;the maximum Sm deposit content by PC (γ=0.1, T_(on)=0.05 ms) was 9.5 at% (1900 mA/cm²) which was less than by DC (Sm=18.5 at % at 600 mA/cm²).At 60° C., although PC had higher PCD_(max), the increase rate in Smcontent for PCD (or CD)

$\frac{{SMcontent}}{{{PCD}}\mspace{11mu} \left( {{or}\mspace{14mu} {CD}} \right)},$

was much lower for PC than for DC leading to this result. To sum up, at25° C., a higher maximum Sm deposit content was obtained by PC than byDC electrodeposition; at 60° C., DC had a higher maximum Sm depositcontent than PC.

Effect of T_(on): T_(on), relates to the total charge passed per pulsecycle; the longer T_(on), the more charge passed for electrochemicalreactions. All the deposits were obtained from 25° C. bath 1; theexperimental conditions are given in Table 13; and the Hull cellpatterns of deposits are shown in FIG. 39.

TABLE 13 The effect of T_(on) T_(off) Duty Frequency T PCD_(max) EXP #Bath T_(on) (ms) (ms) Cycle (Hz) (° C.) (mA/cm²) 49 1 0.05 0.45 0.1 2k25 1100 50 0.1 0.9 1k 1100 51 1 9 100 380 52 10 90  10 200 *Total charge= 50 C, substrate area = 7.5 cm² (10 cm × 0.75 cm), no agitation;applied peak current = 4.5 A.

At shorter T_(on) higher PCD_(max) were obtained (FIG. 39). ShorterT_(on) resulted in lower Sm deposit content but since the metallicregion was significantly extended (greater PCD_(max)), higher Sm contentcould be obtained. Deposits obtained from 25° C. bath 1 for T_(on)=0.1ms, duty cycle=0.1, for instance, had 22 at % Sm content at 650 mA/cm²(FIG. 40).

(14) Effect of Duty Cycle

Bath 1 was used to study the effect of duty cycle on electrodepositedCo—Sm alloys; experimental conditions are given in Table 14 and FIG. 41show their Hull cell patterns.

TABLE 14 The effect of duty cycle T_(on) T_(off) Duty Frequency TPCD_(max) EXP # Bath (ms) (ms) Cycle (Hz) (° C.) (mA/cm²) 112 1 0.1 1.900.050 500 25 1300 111 1.23 0.075 750 1250 50 0.9 0.1 1k 1100 83 0.4 0.22k 160 84 0.23 0.3 3k 80 3 0 1 DC 50 (continuous) *Total charge = 50 C,substrate area = 7.5 cm² (10 cm × 0.75 cm), no agitation and appliedpeak current = 4.5 A.

Smaller duty cycle led to higher PCD_(max) For example, PCD_(max)dramatically increased from 50 to 1300 mA/cm² by decreasing duty cyclefrom 1 to 0.05 (FIG. 41); Sm deposit content decreased (FIG. 42). Fordeposits obtained at 600 mA/cm², Sm deposit content decreased from 21 to7.5 at % by decreasing the duty cycle from 0.1 to 0.05.

3. Parametric Aqueous Electrodeposition Studies of Co—Sm Alloys

Iron group (IG)-rare earth (RE) alloys are known for their ferromagneticand energy storage applications and resistance to aggressiveenvironments. Co—Sm alloys, such SmCo₅ and Sm₂Co₁₇, have already beencommercialized for their high performance magnetic properties. Thesefilms have been prepared by sputtering [H. C. Theuerer, E. A. Nesbittand D. D. Bacon, J. Appl. Phys., 40, 2994 (1969).], evaporation [V.Geiss, E. Kneller and A. Nest, Appl. Phys., A27, 79 (1982).], and plasmaspraying [K. Kumar, D. Das and E. Wettstein, J. Appl. Phys., 49, 2052(1978).].

SmCo₅ alloys have very large coercivities as a result of itsconsiderable magnetic anisotropy constant (ku) of about 10⁷J/m³, andthey also have high Curie temperatures. The latter enables highoperating temperatures for permanent magnet applications as in magneticcoupling, sensors, nano and micro systems, servo motors, etc. AlthoughCoSm alloys are expensive, their superior high temperature magneticperformance and reliability outweigh the costs for military andaeronautical/aerospace applications [M. Rassignol and J. P. Yonnet,Magnetism, II-Materials and Applications, E. T. de Lacheisserie, D.Gignoux and M. Schlenker, Eds., Chap. 15, Kluwer Academic Publishers,The Netherlands (2002).]. The development of an aqueouselectrodeposition process for Co—Sm alloys will substantially lowermanufacturing costs.

The high perpendicular coercivities of Co—Sm alloys make them eminentlysuitable for ultra high density information storage as in hard diskdrives [M. H. Kryder, Applied Magntism, R. Gerber, C. D. Wright and G.Asti, Eds., p. 39, Kluwer Academic Publishers, The Netherlands (1994);R. C. O'Handley, Modern Magnetic Materials, Chaps. 13 & 17, John Wiley &Sons Inc., New York (2000); J. Sayama, K. Mizutani, T. Asahi, J. Ariake,K. Ouchi, S. Matsumura and T. Osaka, J. Magn. Magn. Mater., 287, 239(2005).]. Iwasaki and Nakamura had earlier proposed (1977) perpendicularmagnetic recording [S. Iwasaki and Y. Nakamura, EEE Trans. Mag., MAG-13,1272 (1977).], and it has now been commercially realized.

Like other rare earth metals, electrodeposition of metallic samariumfrom aqueous electrolytes has not been achieved. Similarly, refractorymetals such as W, Mo and V also have not been electrodeposited fromaqueous media. However, electrodeposition of these metals fromnonaqueous media can be done [N. Usuzaka, H. Yamaguchi and T. Watanabe,Mater. Sci. Eng., A99, 105 (1988).]. Although pure metals of W, Mo and Vhave not been electrodeposited from aqueous media, electrodeposition ofalloys of W and Mo with the iron group metals (Ni, Fe, Co) have beenreadily done for over 60 years [M. L. Holt and M. L. Nielsen, Trans.Electrochem. Soc., 82, 193 (1942); H. J. Seim and M. L. Holt, Ibid, 96,205 (1949).], IG-V binary and ternary magnetic thin film alloys byelectrodeposition from aqueous solutions have been reported recently [C.Arcos, M. Schwartz and K. Nobe, Plat. Surf Finish., 90 (6), 46 (2003).].

More recently, IG-RE alloy electrodeposition from aqueous media has beenachieved by our group by the use of glycine and other aminocarboxylatesas complexers [L. Chen, M. Schwartz and K. Nobe, Proc. Electrochem.Soc., PV96-19, 239 (1996); M. Schwartz, F. He, N. Myung and K. Nobe,Ibid., PV98-20, 646 (1999); N. Myung, M. Schwartz and K. Nobe, Ibid.,PV99-33, 263 (1999); M. Schwartz, N. Myung and K. Nobe, J. Electrochem.Soc., 151 (7), C468 (2004). 17. H. S. Cho, IEEE Trans. Magn., 33 (5),2890 (1 997).]. The metal ions and glycine are known to faunhetero-nuclear glycinato coordinated complexes in aqueous solutions.

a. Experimental

Unless otherwise noted, the plating solutions consisted of 1M samariumsulfamate, 0.05M cobalt sulfate, 0.15M glycine as the complexer and 1Mammonium sulfamate as the conducting salt; also the total charge passedwas 50 coulombs. The pH value of the plating bath was 5.2 as measured at25° C. Various current densities and bath temperatures (25-60° C.) wereused to obtain deposits; solutions were not agitated duringelectrodeposition.

An EG&G PAR potentiostat, model 173, served as the power source forelectrodeposition. Brass panels (2×1.9 cm) served as cathodes and aplatinum sheet (3×6 cm) was used as the anode. The brass panels weremechanically cleaned, soaked in alkaline solution for 10 min., rinsed indeionized water and immersed in 10% HCl for 30 seconds.

The ratios of the samarium and cobalt deposit content was determined byenergy dispersive x-ray analysis (EDX); deposit content of cobalt wasalso determined by atomic absorption spectrophotometry (AA). Themicrostructure, crystal orientation and grain size were determined byx-ray diffraction (XRD) and surface morphology by scanning electronmicroscopy (SEM). Magnetic properties were determined by a vibratingsample magnetometer (VSM), model 1660 ADE Tech.).

b. Results and Discussions

The experimental data presented in the figures are for deposits whichhad metallic appearance. In each case, at higher current densities (CD),deposits were non-metallic and these results are not shown.

FIG. 43 shows the effect of increased solution temperature on theapplied CD range. At 25° C., the effective CD for metallic deposits waslimited to 350 mA/cm², whereas for a solution temperature of 60° C., theCD could be increased to 700 mA/cm², resulting in increasing deposit Smcontent from 8 to 17 at %. Although the (linear) deposition rate wasgreater at 25° C., extrapolation indicated that at 450 mA/cm² thedeposition rate at 60° C. would have exceeded that of the rate at 25° C.Elevated solution temperatures permit higher CDs depositing metallicappearing deposits with deposit Sm content reaching 17.2 at % at CD˜700mA/cm² and a temperature of 60° C. The current efficiencies (CE) dropsharply between 50 mA/cm² (20%) and 200 mA/cm² (6%) with little changebetween 200 mA/cm² and 350 mA/cm² in the 25° C. solution, whereas the CEdecreases almost linearly in the 60° C. solution with an apparent slopeof about 1%/100 mA/cm² (FIG. 44).

With increasing solution temperature from 25-60° C., the deposit Smcontent decreases almost linearly for CDs of 100 mA/cm² and 300 mA/cm²,the latter being consistently 4% higher (FIG. 45). However, the CEs werehigher for the lower applied CD (FIG. 46).

Additional parametric studies were performed to assess the effects ofagitation, the solution concentration of Sm sulfamate and glycine, andthe presence of NH₄ sulfamate on the deposit Sm content. Agitation had agreater effect on the deposit Sm content at higher CDs while itgenerally increased with decrease in solution concentration of the Smsalt from 1M. An increase in the glycine concentration from 0.15Mdecreased the deposit Sm content. Addition of the conducting salt (NH₄sulfamate) decreased the deposit Sm content.

Magnetic saturation (Ms) values of the electrodeposits are quite closebut slightly lower than those of sputtered Co—Sm thin films atequivalent Sm contents (FIG. 47). This is indicative of the metallicnature of the electrodeposited Co—Sm alloys. The electrodepositionresults in this figure were obtained from solutions with no conductingsalt (NH₄sulfamate). The closed circle points represent electrodepositsobtained at 60° C. with 50 coulombs of charge passed. The open pointsrepresent thicker deposits (500 coul. charge passed). Higher Sm contentcould be obtained for thicker deposits from solutions in the absence ofNH₄sulfamate (˜33 at. % Sm, open diamonds) than in its presence (23 at.%Sm, closed circles). Pulse current electrodeposition (open triangles)produced metallic deposits (20 at. %Sm) for a duty cycle (7) of 0.1.Magnetic saturation of non-metallic deposits were substantially lowerthan metallic deposits of the equivalent Sm content. For example, for 17at %Sm, Ms of the metallic deposit was 4 times higher than thenon-metallic deposit. FIG. 48 shows that the deposit coercivities (Hc)in the parallel direction increase only slightly with increase indeposit Sm content, i.e., with increased CD, and is not affected bysolution temperature. However, deposit coercivities decrease sharply inthe perpendicular direction with increasing CD in deposits from 25° C.solutions, but a linear decrease with a negative slope from 60° C.solutions. Perpendicular coercivities are significantly higher than inthe parallel direction. Thus, heat treatment of Co—Sm deposits leads tosubstantially higher coercivities.

The deposit topography is affected by the applied CD and probably alsosolution temperature. There is increased surface roughness as a resultof increased CD. FIGS. 49 a,b show that the absence of the conductingsalt (NH₄sulfamate) dramatically results in a much smoother surface thanin its presence. X-ray diffraction spectra (XRD) (FIG. 50) indicate the2.1 at. % Sm deposit (100 mA/cm²) appears amorphous and the 10.4 at. %Sm deposit (500 mA/cm²) exhibits crystalline structures with (200) phaseof Sm₂Co₁₇ alloy composition. In the absence of NH₄ sulfamate in thebath, the (201) phase of the SmCo₅ alloy as well as the Sm₂Co₁₇ (200)phase appear in the deposits.

c. Conculsions

Sm content of metallic deposits of Co—Sm can be increased at higher CDsfrom higher temperature solutions. Furthermore, significantly higherdeposit Sm content can be obtained from solutions in the absence than inthe presence of the conducting salt (NH₄ sulfamate). Co—Sm deposits with33 at % Sm have been obtained at 500 mA/cm² and a solution temperatureof 60° C. Magnetic saturation of electrodeposits were close to those ofsputtered deposits. Perpendicular coercivities were substantially higherthan parallel coercivities for Co—Sm electrodeposits. Heat treatment ofdeposits should result in an order of magnitude increase inperpendicular coercivities.

4. Coordination Chemistry in the Electrodeposition of IG-V, W and MoAlloys from Aqueous Carboxylate Solutions

Polycarboxylates, hydroxycarboxylates and aminocarboxylates are wellknown additives functioning as complexing agents for theelectrodeposition of single metals and alloys from aqueous platingbaths. Tartrates and citrates are extensively employed inelectrodeposition of alloys, including the deposition of alloyscontaining elements such as the refractory metals: W, Mo, V. Althoughthese individual metals cannot be electrodeposited from aqueous media,alloys with the iron group metals (IG) have been electrodeposited fromaqueous solutions [A. Brenner, Electrodeposition of Alloys, Vol. II,.Acad. Press (1963).

Brenner et al. and Holt and his co-workers have studied theelectrodeposition of IG-W and —Mo alloys from aqueous solutions [A.Brenner, P. Burkheard and E. Seegmiller, J. Iles. NBS, 94, 351 (1947);L. E. Vaaler and M. L. Holt, Trans. Electrochem. Soc. 90, 43 (1946); L.E. Vaaler and M. L. Holt, Ibid., 94, 50 (1948); W. E. Clark and M. L.Holt, Ibid., 94, 244 (1948); M. H. Lietzke and M. L. Holt, Ibid., 94,252 (1948); R. F. McElwee and M. L. Holt. I Electrochem. Soc., 99 (2),48 (1952).]. More recent work on the electrodeposition of IG-X alloyshas been reported for electroplating baths containing citrates ascomplexers, with some consideration given to the nature and structure ofthe organometallic complexes involved [M. Schwartz, C. Arcos and K.Nobe, Plat. Surf. Fin., 90 (6) 46 (2003); E. J. Podlaha and D. Landolt,J. Electrochem. Soc., 143, 885 (1996); Ibid., 143 (11) 893 (1996);Ibid., 144 (5) 1672 (1997); O. Younes and E. Gileadi, Ibid., 149, C100(2002); O. Younes-Metzler, L. Zhu and E. Gileadi, Electrochim. Acta, 48,2551 (2003).]. There has been a growing interest in determining thestructures of these refractory metal-hydroxycarboxylato—complexes byspectroscopic experiments for biological, physiological applications [M.Tsaramyrsi, M. K. aliva, A. Salifoglou, C. P. Raptopoulou, A. Terzis, V.Tangoulis and J. Giapintzakis, Inorg. Chem., 40 (23), 5773 (2001); T.Kiss, P. Buglyo'. D. Sanna, G. Micera, P. Decock and D. Dewaele, Inorg.Chem. Acta, 239, 145 (1995); 9. Z-H Thou, H-L Wan and K-R Tsai, 1 Chem.Soc., Dalton Trans., 4289 (1999). Z-H Thou, H-L Wan and K-R Tsai, Inorg.Chem., 39, 59 (2000); Z-H Thou, S-Y Hou and H-L Wan, J. Chem. Soc.,Dalton Trans., 1393 (2004).].

Since the early 1990s, this laboratory has been investigating theelectrodeposition of IG-V alloys in order to improve the physicalproperties as well as the corrosion resistance of the high magneticmoment 90Co10Fe alloys, as suggested by Liao [S. H. Liao, IEEE Tran.Magn 23, 2981 (1987).]. In addition, the electrodeposition ofV-Petinendur (49Co49Fe2V) was investigated because of its excellentmagnetic properties; it has not had wide commercial applications becauseof its high manufacturing costs, however [G. Y. Chin and J. H. Wernickin Ferromagnetic Materials, vol. 2, p. 168, E. P. Wohlfarth, Ed.,North-Holland, Amsterdam, (1980).]. Development of a commercialelectrodeposition process would sharply reduce these costs and greatlyexpand applications in miniaturized electronic devices.

Some of our interest in the electrodeposition of the IG-X alloys (X=V. Wand Mo) dates to the early work (1948) of one of us (M. S.) whodeveloped a commercial Co—W plating process using an ammoniacal citratebath. He found that when the Co and WO₄ ²⁻ salt solutions are mixed, acobalt tungstate precipitate forms which dissolves with the addition ofcitrate. His experimental results lead him to conjecture that bothCo(II) and W(VI) are coordinated in the same complex with deprotonationof the carboxylate forming a heteronuclear biscitrato—complex.Subsequently, later work by Zhuravleva and co-workers on thecomplexation of oxyvanadium and IG ions with citric acid indicated theexistence of homo-dinuclearVO-biscitrato- and hetero-dinuclearIGbiscitrato- complexes [Y. I. Sal'nikov, F. V. Devyatov, N. E.Zhuravleva, D. V. Golodnitskaya, Jh. Neorgan Khimi., 29, 2273 (1984); A.N. Glebov, Y. I. Sal'nikov, N. E. Zhuravleva, V. V. Chevela and P. A.Vasil'ev, Ibid., 27, 2146 (1982); N. E. Zhuravleva and Y. I. Sal'nikov,Proc. Tech. Inst. Chem. and Chem Tech., 32 (2) 25 (1989).].

Plating baths are presented in Table 15, Table 16, Table 17, and Table18. NH₃ (aq) and HCl (or sulfamic acid) were used to adjust solution pH.Plating baths were maintained at room temperature and were quiescent ormechanically stirred, as required. DC was provided by a PAR potentiostator a Kraft Dynatronix power supply (Model DPR 20-5-10). Total chargepassed was controlled to produce desired film thicknesses.

Brass panels served as cathodes and the anode was a cobalt (or Pt)sheet. The brass panels were scrubbed with Alconox, rinsed in deionizedwater and then activated in concentrated HCl. The deposits weredissolved in concentrated HNO₃ for analysis. Cobalt and vanadium depositcontents were determined by atomic absorption spectrophotometry (AA).Cobalt was also determined by energy dispersive spectroscopy (EDX).Tungsten and molybdenum were analyzed by gravimetric methods as well asEDX. Scanning electron microscopy (SEM) and x-ray diffraction were usedto characterize the deposits. Magnetic properties of the electrodepositswere obtained with vibrating sample magnetometer (VSM) (ADETech, Model1660).

a. IG-Rare Earth (SM) Coordination Compounds

Initial investigation of the electrodeposition of IG-RE alloys wasreported in 1996 [L. Chen, M. Schwartz and K. Nobe, in ElectrodepositedThin Films. M. Paunovic and D. A. Scherson, Editors, PV96-19, p. 239,The Electrochem. Soc. Proceedings Series, Pennington, N.J. (1996).].Hydroxycarboxylate and other carboxylate salts as complexers appeared tobe inferior to glycine and other amino acid salts. The bipolarity, i.e.zwitterionic properties, of glycine (and other aminoacids) results inionic complexes at the cathode surface as the pH fluctuates. As aresult, structures and deposition mechanisms of IG-RE dinucleardiglycinato- and triglycinato-coordination complexes have beenconsidered as the vehicles for the co-deposition of the IG-RE alloys [M.Schwartz, M. V. Myung and K. Nobe, J. Electrochem. Soc., 151. C468(2004).]. Continued development indicates the deposit Sm contents andresulting magnetic properties could be varied, depending on the solutioncomposition, CD and temperature [J. C. Wei, M. Schwartz and K. Nobe,Trans. Electrochem. Soc. (in press).]. Table 15 summarizes typicalsolution composition ranges and with the deposition conditions selected,result in wide variations in deposit Sm content. The glycine: Co ratioin these solutions was 3:1 with Sm³⁺ concentration in excess. Solutionswith lower Co and Sm concentrations resulted in higher deposit Smcontents (15-18 a/o) than more concentrated solutions. In the lattersolution, FIG. 51 shows the deposit Sm content increased linearly withincreasing CD while the CE decreased sharply as CD increased to ˜100mA/cm², reaching a plateau with increased CD, indicating a possiblerelation of hydrogen evolution to deposit content.

TABLE 15 Representative plating baths for Co—Sm alloys Co²⁺ (assulfamate) 0.06M-0.12M Sm³⁺ (as sulfamate)  0.3M-0.9M Glycine0.18M-0.36M NH₄(NH₂SO₃) 1.0M NH₄OH pH 6.5-7.0

TABLE 16 Representative plating baths for IG-V alloys Binary TernaryCo²⁺ 0.3M 0.15-0.3 M VO²⁺ 0.15-0.3 0.15-0.17 M Fe²⁺ 0.03M-0.15M (Ni²⁺)(0.05M) Na₃C₆H₅O₇ 0.25-0.35 M 0.25 M H₃BO₃ 0.1 M NH₄Cl 1.0 M NH₄OH pH6.0-7.5

b. IG-Vanadium Coordination Compounds

Electrodeposition of binary and ternary IG-V alloys from citratesolutions has been reported [M. Schwartz, C. Arcos and K. Nobe, Plat.Surf. Fin., 90 (6) 46 (2003); B. Y. Yoo, dissertation, UCLA, 2003; alsounpublished data, UCLA. 2004.]. Although “representative” solutioncompositions are given in Table 16, wide variations in concentrationsprovide flexibility in the resulting deposit compositions and theirmagnetic properties. In binary alloy deposits, the V contents decreased:Co>Fe>Ni and the magnetic properties varied with the deposit V content;magnetic saturation decreased and coercivities increased with increasingdeposit V content (Table 19). Thus, the ability to control depositcomposition and their magnetic properties provides “tailor-made”deposits for various electronic applications. FIG. 52 indicates the widevariations in Co—V electrodeposits vs CD with deposit Co contentincreasing with increasing CD, whereas Fe-V electrodeposits exhibit verylittle change in deposit compositions vs CD, with deposit V contents <2w/o over the CD range, 5-50 mA/cm² [B. Y. Yoo, dissertation, UCLA, 2003;also unpublished data, UCLA. 2004.]. Magnetic saturation, B_(s), ofternary CoFeV electrodeposits exceeded that of the binary CoV and FeVelectrodeposits. Ternary 48Co49.8Fe2.2V electrodeposits approximatingbulk 2V-Permendur (48Co48Fe2V) exhibited a magnetic saturation B_(s) of2.32 T. Liao indicated a 90Co 10Fe electrodeposit had a magneticsaturation of 1.9 T, exceeding that of Permalloy (80Ni20Fe), B_(s)=1.0T; however, corrosion resistance of the alloy was inferior [S. H. Liao,IEEE Tran. Magn 23, 2981 (1987).]. As shown in Table 19, addition of Vto the binary electrodeposit (87.3Co8.6Fe4.1V) improved corrosionresistance and increased magnetic saturation, B_(s)=2.20 T [B. Y. Yoo,dissertation, UCLA, 2003; also unpublished data, UCLA. 2004.].

TABLE 17 Representative plating baths for Co—W alloys Brenner Holt (3)(2) Brenner (2) MS (12) Gileadi (6) [Co²⁺] (M) 0.213 0.6 0.42 0.12 *(Ni)[WO₄ ²⁺] (M) 0.213 0.3 0.13 0.12 * [Cit³⁻] (M) 0.314 1.2 — 0.48 *[Tart²⁻] (M) — — 1.42 — — NH₄Cl — 0.5 0.94 0.5  * NH₄OH 7-8.5 8.5 8.58.5-9    8 (pH) % W, a/o >17.5 7.7 7.7-9.6  7.9-17.5 12-15 % W, w/o >40~20 20-50 20-40 30-35 T (° C.) 70 ≧40 ≧90 65-80 25

TABLE 18 Representative plating baths for IG-Mo alloys Holt (22) Landolt(5) IG [Fe³⁺], [Co²⁺], [Ni²⁺] (M) 0.3 0.2 (Ni) Na₂MoO₄ (M) 0.02-0.0750.005-0.05  Na₃C₆H₅O₇ 0.3 0.25-0.95 NH₄OH (pH) 10.5  9.7-10.2 T (° C.)25 25-40

TABLE 19 Magnetic properties of selected electrodeposited IG-V, W, Moalloys Co Bs (wt %) Fe (wt %) V (wt %) W (wt %) Hc (Oe) (T) Reference 919 118 1.43 (20) 97.8 2.2 25 1.93 (20) 67 33 57 1.28 (19) 87.3 8.6 4.1 582.20 (20) 48.0 49.8 2.2 46 2.32 (20)

Nikolova and Nikolov suggested mononuclear and dinuclear oxyvanadiumcitrato complexes. Based on indirect evidence, potentiometricexperiments and IR spectra, they indicated the protonated hydroxo-groupmay be involved in 1:1 mononuclear citratocomplex (stabilityconstant=6.6×10⁸) and a dinuclear citrato- complex with the hydroxygroup or carboxylato group bridging the two VO's (stabilityconstant=3.2×10¹¹) [B. M. Nikolova and G. St. Nikolov,./.Inorg. Nucl.Chem., 29, 1013 (1967).].

Zhuravleva and co-workers studied dinuclear IG biscitrato-complexes andheteronuclear IG-(VO)₂-biscitrato-complexes [Y. I. Sal'nikov, F. V.Devyatov, N. E. Zhuravleva, D. V. Golodnitskaya, Jh. Neorgan Khimi., 29,2273 (1984); A. N. Glebov, Y. I. Sal'nikov, N. E. Zhuravleva, V. V.Chevela and P. A. Vasil'ev, Ibid., 27, 2146 (1982); N.E. Zhuravleva andY. I. Sal'nikov, Proc. Tech. Inst. Chem. and Chem Tech., 32 (2) 25(1989).]. Salni'kov et al. investigated mononuclear, dihomonuclear andheteronuclear biscitrato-complexes of Ni and Co, the latter beingpartially deprotonated or completely deprotonated [Y. I. Sal'nikov, F.V. Devyatov, N. E. Zhuravleva, D. V. Golodnitskaya, Jh. Neorgan Khimi.,29, 2273 (1984).]. Glebov et al. indicated dinuclear (VO)₂ complexesonly with hydroxocarboxylic acid, e.g., citric, tartaric and malic acids[A. N. Glebov, Y. I. Sal'nikov, N. E. Zhuravleva, V. V. Chevela and P.A. Vasil'ev, Ibid., 27, 2146 (1982).]. The depicted dinuclearbiscitrato-coordination compound indicates protonated hydroxy groupoxygens bridging the two V atoms. Zhuravleva and Salni'kov obtained aheteronuclear biscitrato complex by reacting individual Cu citrate andVO citrate solutions [N. E. Zhuravleva and Y. I. Sal'nikov, Proc. Tech.Inst. Chem. and Chem Tech., 32 (2) 25 (1989).].

c. IG-W Coordination Compounds

Holt and his students investigated the electrodeposition of IG-W alloysfrom ammoniacal citrate solutions [L. E. Vaaler and M. L. Holt, Trans.Electrochem. Soc. 90, 43 (1946); L. E. Vaaler and M. L. Holt, Ibid., 94,50 (1948); W. E. Clark and M. L. Holt, Ibid., 94, 244 (1948); M. H.Lietzke and M. L. Holt, Ibid., 94, 252 (1948); R. F. McElwee and M. L.Holt. I Electrochem. Soc., 99 (2), 48 (1952).]. After complexation,atomic hydrogen reduction has been suggested to explain theco-deposition of IG-W alloys by proposing a two-step reductionhypothesis involving alternating deposition of the IG species whichcatalyzed the reduction of the tungstate ion and resulted in a laminardeposit, based on polarographic studies and cathode potentialmeasurements, the latter being lower in solutions containing tungstateions.

Younes and Gileadi concluded a heteronuclear Ni-W monocitrato complexwith the carboxylate triply deprotonated is the precursor for theelectrodeposition of the Ni—W alloy [O. Younes and E. Gileadi, Ibid.,149, C100 (2002); O. Younes-Metzler, L. Zhu and E. Gileadi, Electrochim.Acta, 48, 2551 (2003).]. The complex is the result of the reaction ofindividual Ni and W citrate complexes. A similar reaction with aNi-biscitrato-complex was considered unlikely because both reactingcomplexes would be highly charged. They also reported that eliminationof NH₄ salts and NH₃ (aq.) from similar solutions resulted in amorphousdeposits with increased deposit W contents, but substantial CEreduction.

Brenner et al. indicated an inorganic Co—W solution (no citrate)resulted in deposits containing 20-27 wt.% W at CDs 20-50 mA/cm²,respectively [A. Brenner, P. Burkheard and E. Seegmiller, J. Iles. NBS,94, 351 (1947).]. Without the presence of NH₄ salts, the solubility ofCo and W is reduced and the CE is quite low, making the solutionunsuitable for practical applications. In the tartrate complexed Co—Wsolution (Table 17), the presence of alkali cations (Na, K tartrate)resulted in diminished deposit W contents as compared to ammoniumtartrate solutions, another indication of the positive effect of thepresence of NH₄ ions.

d. IG-Molybdenum Coordination Compounds.

Holt and students extended their studies of the electrodeposition ofIG-W alloys to IG-Mo alloys from equivalent solution compositions, asshown in (Table 18), [J. Seim and M. L. Holt, Trans. Electrochem. Soc.,95, 205 (1949); D. W. Ernst, R. F. Amlie and M. L. Holt, J. Electrochem.Soc., 102 (8), 461 (1955); D. W. Ernst and M. L. Holt, Ibid., 105 (11),686 (1958).]. Initially, Hull Cells were utilized to determine pH,temperature and CD ranges for bright, metallic deposits and resultingdeposit composition and CEs. Various ligands were classified as “good”or “poor”: For Ni—Mo, citrate and tartrate were considered “good”; forCo—Mo, the “good” ligands were extended to include malate (and malicacid) and glycolic acid. Sodium citrate was considered superior tocitric acid or ammonium citrate.

Similar to IG-W electrodeposition, deposit Mo contents varied with theco-deposited IG metal: Fe (59%)>Co (40%)>Ni (20%). The CEs wereinversely related to the deposit Mo contents: Ni (75-85%)>Co (50-60%)>Fe(10-20%), which seems to indicate a role for adsorbed hydrogen atoms inthe deposition process.

Podlaha and Landolt studied the effect of varying the solution Ni:Moratios on mass transport and kinetically controlled processes withrotating cylindrical electrodes [E. J. Podlaha and D. Landolt, J.Electrochem. Soc., 143, 885 (1996); Ibid., 143 (11) 893 (1996); Ibid.,144 (5) 1672 (1997).]. In addition to the metal salts, the ammoniacalsolution contained sodium citrate; no conducting salts were added (Table18). The concentration of NH₃ (aq.) appears to be critical with respectto the deposit Mo content. “High” NH₃ (aq.) concentrations resulted inhigh CEs 90% and lower deposit Mo content; most of the data presentedwere obtained with 0.28 M NH₃ (aq.). A deposition mechanism whereby Mois deposited from an intermediate (Ni—Mo) complex either adsorbed ordissolved in the solution is proposed with Ni depositing independentlyand considered the catalyst for the electrodeposition of the alloy. Themodel is extended to include codeposition of Co—Mo and Fe—Mo and explainthe differing effects of the IG species on the deposit Mo content byincluding the additional presence of a single IG complex with a two-stepreduction.

Zhou and collaborators prepared and determined the structures of variousMo, W, and V citrato-coordination compounds, which are precursors toFeMo cofactors in nitrogenase protein catalysts, using IR and NMRspectroscopies and Xray diffraction [9. Z-H Thou, H-L Wan and K-R Tsai,1 Chem. Soc., Dalton Trans., 4289 (1999). Z-H Thou, H-L Wan and K-RTsai, Inorg. Chem., 39, 59 (2000); Z-H Thou, S-Y Hou and H-L Wan, J.Chem. Soc., Dalton Trans., 1393 (2004).]. Tridentate Binuclearbiscitrato-complexes convert to bidentate mononuclear biscitrato ionswith excess citric acid (pH 3.5). Each ligand is coordinated as abidentate ligand through the deprotonated central carboxylato- andvicinal hydroxy-groups with the terminal carboxylate groups uncomplexed.The structure of the tridentate citratocomplexes depends on the degreeof protonation of the reacting ligand and solution pH. Mononuclearmonocitrato-complex converts to dinuclear biscitrato-complex with thetwo metal atoms connected via an oxygen bridge and two oxygen atomscovalently bonded to each metal atom in lower pH solution with valenciesdepending on whether or not the terminal carboxylate groups areprotonated.

e. Structure of IG-RE-Glycine Complexes

The zwitterionic structure of glycine (gly) protonates or deprotonatesdepending on the solution pH, as shown FIG. 53 a. Glycine usuallycoordinates through the carboxylate groups forming O-M-O bonds; it canalso form O-M-N and N-M-N bonds [C. P. Sinha, Complexes of the RareEarths, Pergamon Press, 1966.]. Single metal (i.e., IG²) complexes areprobably mononuclear monoglycine bidentate chelate complexes. For homo-or hetero-dinuclear complexation, multiligand complexes are requiredthrough N-MI-N and O-M₂-O bonds. Both IG and RE cations are likely in ahetero-dinuclear trisglycine complex as in FIG. 53 b. However, becauseof the bipolar character of glycine, it can simulate polymerization byelectrostatic attraction between deprotonated zwitterions, mimicing dipeptide or trip eptide structures through O—N “bonds”. In the case of theheteronuclear IG-RE complex, quasi-digly (FIG. 53 c) or trigly (FIG. 53d) complexes can be formed and adsorbed at the cathode surface as thecathode film pH fluctuates.

f. Structure of IG-VO-Biscitrate Complexes

Citric acid can form di-, tri- or tetra-dentate complexes with metalions, depending on the degree of deprotonation. The structure of thebinary IG-VO citrate complex (FIG. 54 a) has one carboxylate groupprotonated with the hydroxy-hydrogen of each citrate ligand attracted tothe VO, possibly forming H-bonds. The depicted complex structure showspartial deprotonation of the citrate moiety, resulting in a zero-valentcomplex. With continued deprotonation, the complex becomes anionic withincreasing negative charges. Thus, the degree ofprotonation/deprotonation of the carboxylatogroups is dependent onsolution pH. As the pH in the cathode film fluctuates slightly, theforms of the coordination complex may equilibrate. FIG. 55 a indicatesthe hydroxy hydrogen from each citrate ligand reacts with theoxyvanadium (VO) component in step 2, leaving the IG-V citrate complex[IG^(II)V^(IV) (C₆H_(S)O₇)₂]⁰ to be step-wise reduced by hydrogen atomsto deposit the IG-V alloy.

FIG. 54 b shows the structure of the ternary IG-IG-V-citrate complex.After removal of the oxygen in the oxyvanadium (VO) component, as thebinary complex, a similar sequential reduction process occurs toelectrodeposit the ternary alloy (FIG. 55 b).

g. Structure of IG-W (Mo) Biscitrate Complexes

The tungstate (molybdate) ion reacts with citric acid and the Id′ ion toform the IG-W(Mo) citrate complex (FIG. 56). Similar hydroxy-H bonds andreacts with one ofthe (M^(vI)00) oxygens converting to the complex[IG^(II)M^(VI) O(C₆H_(S)O₇)₂]⁰. FIG. 57, as FIG. 55, shows the similarreduction of the IG^(II) and M^(VI) in the IG-M citrate complex to theIG-M alloy.

h. Co—W/CR Composite Coating

Although there is much interest today on product miniaturization, suchas thin film magnetic devices, utilizing these electrodepositedIG-refractory metal alloys from complexed solutions, and the structuresof V, W and Mo (poly)homonuclear and (poly)heteronuclearpolycitrato-complexes for physiological processes, as discussed above,we also point out potential industrial applications for thickerelectroplated alloys, based on physical, mechanical and high temperatureproperties such as corrosion and wear resistance and the ability toundergo hardening with thermal treatment. FIG. 58 illustrates thepotential of producing unique composite electrodeposits for specificapplications. In this example, corrosion resistance, wear resistance andhigh temperature properties were required [M. Schwartz in Handbook ofDeposition Technologies for Films and Coatings, R. F. Bunshah, Ed., Chpt10, Noyes Publ. (1994).]. The composite consists of a 80Co-20W deposit(56 μm) from the solution in Table 17 +Cr from CrO₃/H₂SO₄ solution (30μm)+Co—W (20 μm)+Cr (thin deposit to protect deposit edges). Thespecimens were subjected to high temperature environment in air (todetermine oxidation resistance) and a carburizing atmosphere, attemptingto diffuse C into the Co—W deposit to form and disperse carbide in thedeposit. To obtain good adhesion of these layers, a thin cobalt strike(S) was deposited on the steel substrate and between each deposit toimprove deposit adhesion.

5. Direct Current (DC) Electrodeposition Studies

DC electrodeposition using a parallel electrode system was investigatedto determine, more precisely, the optimum operating and aqueous bathconditions, estimated by the Hull cell studies, to obtain high Smcontent, metallic Co—Sm alloys. The purpose is to obtain stoichiometriccompositions of Co—Sm alloys to form intermetallic Sm₂Co₁₇ (10.5 at %Sm)and SmCo₅ (16.7 at %Sm), and, in addition, Sm₂O₇ (22.2 at %Sm) and SmCo₃(25 at %Sm) after appropriate heat treatment procedures.

DC electrodeposition of Co—Sm alloys from aqueous solutions has beenstudied at various operating conditions (e.g., current densities,temperatures, fluid dynamics and pHs) and plating baths (concentrationof Sm sulfamate, glycine, Co sulfate, NH₄ sulfamate supportingelectrolyte). Morphologies, crystalline structures, preferredorientation and microstructures of deposits from differentelectrodeposition parameters were studied and correlated to theirmagnetic properties.

Samarium deposit content increased with increasing current density.Increased solution temperatures from 25 to 60° C. effectively extendedthe CD to obtain metallic deposits (CD)_(max) from 50 to 500 A/cm²leading to a high Sm deposit content of 32 at % from a bath consistingof 1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine at 60° C. At low CDof 10 & 50 mA/cm² and 25° C., increasing solution pH increased Smdeposit content and then reached a constant. At 60° C., Sm contentincreased with increased solution pH and at 100 and 300 mA/cm², Smcontent reached maximum at pH 5 and 4, respectively. Rotating diskelectrode (RDE) results suggest mass transfer effects in the depositionof Co.

Decreased Sm sulfamate concentration increased Sm deposit content.However, high content of Sm hydroxide/oxide was found indicating thatthe increase of Sm content was due to formation of Sm hydroxide/oxide indeposits. Highest Sm contents were obtained at glycine concentrationbetween 0.1M (glycine: Co²⁺=2:1) and 0.15M (glycine: Co²⁺=3:1). Additionof NH₄ sulfamate resulted in decreased Sm content.

Crystal structures were dependent on Sm content. Deposits changed fromcrystalline to non-crystalline structures by increased Sm depositcontent. Crystal structures of electrodeposited Co—Sm crystallites weredominated by hcp phases. Higher Sm content deposits were usuallyaccompanied with more microcracks due to higher internal stress bylattice distortion. Lower microcrack densities were found in the depositobtained at higher solution temperatures.

Magnetic properties of electrodeposited Co—Sm alloys are stronglydependent on alloy composition, crystal structure and particle size ofdeposits. Increased Sm content resulted in deposits changing fromcrystalline to non-crystalline structures and decreased grain size.Magnetic saturation (Ms) decreased linearly with increased Sm depositcontent and was in agreement with sputtered films. On the other hand,deposits with high oxide/hydroxide content had much lower Ms values. Fordeposits obtained at different conditions, perpendicular coercivityvaried in the range of 150 to 1160 Oe, and parallel coercivityfluctuated between 50 and 150 Oe. Hc decreased sharply but changedlittle in the in-plane direction by increase in Sm content. Thesignificant change in Hc may be the result of the considerable decreasein particle size in the in-plane direction. Parallel squareness (Mr/Ms)were higher than perpendicular squareness indicating the preferredmagnetization direction lies on the deposit plane. Squareness decreasedwith increased Sm content for deposits changing from crystalline tonon-crystalline structures.

In Hull Cell studies, we have already learned about howelectrodeposition parameters qualitatively affected Sm deposit contentand CD_(max) (the maximum CD for metallic deposits region) by Hull cellstudy. In addition, proper plating solutions and operating conditions ofobtaining high Sm content deposit (26 at % Sm) by DC electrodepositionhave also been achieved. In DC electrodeposition studies, we not onlymade deposits by parallel electrodes to confirm the Hull cell resultsbut also studied the impacts of these parameters on the properties ofelectrodeposited Co—Sm alloys. Alloy properties, such as composition,crystal structure, morphology, microstructure and magnetic properties(i.e. coercivity Hc, saturation magnetization Ms and squareness S),varied by DC electrodeposition parameters will be studied andcorrelated. These studies are very helpful for not only getting a betterunderstanding about the dependence of alloy properties onelectrodeposition parameters but also providing important information todevelop the mechanism or the electrodeposition of Co-Sin alloys in thefuture.

To understand the magnetic behavior of the electrodeposited Co—Sm thinfilms, it is necessary to study the dependence of Co—Sm alloycomposition on operating conditions (i.e., current density, solutiontemperature, solution pH, and fluid dynamics) and plating solutions(i.e., concentration of Sm sulfamate, glycine, NH₄ sulfamate and typesof supporting electrolytes) and the dependence of morphology (i.e.roughness, cracks and pitting), crystalline (i.e., crystal structure,orientation, grain size and microstructure) on these parameters, thencorrelate these properties to the magnetic behaviors of electrodepositeddeposits.

At the beginning of each section, the effect of parameter on alloycomposition and current efficiency will be quantitatively measured andanalyzed. The amount of Co and Sm deposition and H₂ gas evolution willbe showed in normalized charge diagrams. The second part mainly focusedon the effect of parameters on crystal structures, orientations, grainsize, morphologies and microstructures of deposits by their XRD patternsand the SEM micrographs. Finally, the effect of parameters on depositmagnetic properties (i.e., Hc, Ms and S) obtained from hysteresis loopsof deposits will be studied and correlated to the other alloy propertiesdiscussed in the first and the second part. Magnetic properties of CoSmalloys as deposited will be revealed in this study.

The goals of the parametric studies of DC electrodeposition were:Confirming Hull cell results and obtaining high Sm deposit content Co—Smalloys; Studying the dependence of alloy properties on electrodepositionparameters; Revealing the dependence of magnetic properties ofelectrodeposited Co—Sm alloys on other alloy properties (i.e., alloycomposition, crystal structures, grain size . . . )

FIG. 59 shows the experimental flowchart of a DC experiment which mainlyincludes four parts: pretreatment of cathode, DC electrodeposition,post-treatment of specimen and characterization. Setup of DCelectrodeposition, rotating disk electrode, design of experiments,pretreatment and post-treatment and characterization and analysis ofspecimens will be described in the following discussion.

a. Setup of DC Electrodeposition

FIG. 60 shows the setup of a DC electrodeposition system. An EG&G PARpotentiostat, model 173, served as the power source forelectrodeposition. A coulometer to measure the total applied chargepassed during the electrodeposition. The deposits were obtained in a 250mL beaker filled with the plating solution. Tapped brass panels with 3.8cm² (2×1.9 cm) deposit area served as cathodes and a platinum sheet (3×6cm) was used as the anode; in this experiment, the distance between thecathode and the anode is 4 cm. A saturated calomel electrode (SCE)served as a reference electrode to measure the cathodic potential duringthe electrodeposition process. A shielding panel with a 2×2 cm openingwindow, designed by the simulation result of ANSYS (a finite elementanalysis software), was placed between the cathode and anode to minimizethe thickness variation of deposit by uniformizing the current densitydistribution on the cathode.

b. Setup of Rotating Disk Electrode (RDE) System

The setup of a RDE system shows in FIG. 61. A brass disk (diameter of6.4 mm) was inserted into the cavity at the bottom of the Teflon rod; acopper rod was inserted into that Teflon rod from the other side and allthe way down to touch the back side of the brass disk to make electricalcontact. The RDE was jointed with a stainless rod by a coupler, and thestainless rod was rotated by a motor through a transmission belt. TheRDE was dipped into the electrolyte with the brass disk facing down tothe Pt panel located at the bottom of the plating cell. The distancebetween cathode and anode is about 2 cm. A SCE served as a referenceelectrode to measure the cathodic potential during electrodepositions.

C. Design of Experiments

In the study of DC electrodeposition, operating conditions, such ascurrent density, temperature, pH, fluid dynamics will be varied. Variouscurrent densities (2-500 mA/cm²), bath temperatures (25-60° C.), pHvalues of plating solutions (2-6), fluid dynamics (RDE. 0-4000 rpm) wereused to obtain deposits. Furthermore, composition of plating baths, suchas the concentrations of samarium sulfamate as metal ions, glycine ascomplexer, and ammonium sulfamate, ammonium chloride and potassiumchloride as conducting salts will be varied for different concentrationsto examine their effects on electrodeposited cobalt-samarium alloys. Theconcentration of cobalt sulfate was constant at 0.05M. Plating bathsused to obtain deposits are showed in Table 20:

TABLE 20 Plating baths of cobalt-samarium alloys Item Bath Sm sulfamateCo sulfate Glycine NH₄ Sulfamate NH₄Cl KCl pH 1 1 1 M 0.05 M 0.15 M 5.72 6 1 M 0.05 M 5.9 3 9 1 M 0.05 M 0.15 M 5.0 4 10 1 M 0.05 M 0.15 M 4.05 11 1 M 0.05 M 0.15 M 3.0 6 12 1 M 0.05 M 0.15 M 2.0 7 13 0.75 M   0.05M 0.15 M 5.8 8 14 0.5 M   0.05 M 0.15 M 5.9 9 15 0.25 M   0.05 M 0.15 M5.9 10 16 1 M 0.05 M 0.05 M 5.9 11 17 1 M 0.05 M 0.10 M 5.8 12 18 1 M0.05 M 0.20 M 5.7 13 19 1 M 0.05 M 0.50 M 5.5 14 8 1 M 0.05 M 0.15 M   1M 5.2 15 20 1 M 0.05 M 0.15 M 0.75 M 5.3 16 21 1 M 0.05 M 0.15 M  0.5 M5.4 17 22 1 M 0.05 M 0.15 M 0.25 M 5.4 18 23 1 M 0.05 M 0.15 M 1 M 5.519 24 1 M 0.05 M 0.15 M 1 M 5.6 (The pH values of the plating baths weremeasured at 25° C.; the pH values of bath 9, 10, 11 and 12 were adjustedby sulfamic acid.)

Bath 12, 11, 10, 9 and 1 were used to study the effects of pH from 2 to6; bath 15, 14, 13 and 1 were used to study the effects of theconcentration of samarium sulfamate from 0.25 to 1M; bath 18, 19. 1, 16and 17 were used to study the effects of the concentration of glycinefrom 0.05 to 0.5 M; bath 1, 22, 21, 20 and 8 were used to study theeffects of the concentration of ammonium sulfamate from 0 to 1 M; bath8, 23 and 24 were used to study the effects of different types ofconducting salts in the plating baths.

d. Pretreatment and Post-Treatment

Before electrodeposition, the brass panels were mechanically cleaned,soaked in 0.1M NaOH solution for 10 min., rinsed in deionized water,immersed in 10% HCl for 30 seconds and than rinsed with deionized water.Unless otherwise noted, the total charge passed was 50 coulombs;solutions were not agitated during electrodeposition (except in therotating disk electrode, RDE).

After the deposition of Co—Sm alloys for 50 coulombs, the deposits wereremoved from plating solution, rinsed with deionized water, and driedwith nitrogen gas. Disk-shaped specimens of diameter of 6.4 mm (specimenarea=31.7 mm²) were die-punched out from deposits for analysis.

e. Characterization and Analysis

The samarium

$\frac{Sm}{{Sm} + {Co}}\left( {{at}\%} \right)$

and cobalt deposit content

$\frac{Co}{{Sm} + {Co}}\left( {{at}\%} \right)$

were determined by an energy dispersive x-ray spectroscopy (EDS) with aKevex detector in a Cambridge SEM (see characterization section in HullCell studies); the mass of deposited cobalt was measured by aPerkinElmer flame atomic absorption spectrometer (AA, mode 631); thecrystal structure, orientation, phase identification and grain size weredetermined by a PANalytical x-ray diffraction system (XRD, model X'PertPro) (see characterization section in Hull Cell studies); the surfacemorphology, microstructure and grain size were observed by a JEOLscanning electron microscopy (SEM, model JSM-6700F); magnetic propertieswere determined by a ADE Tech. vibrating sample magnetometer (VSM, model1660). Unless otherwise noted, the experimental data presented indiscussion sections are restricted to deposits with a metallicappearance.

f. Flame Atomic Absorption Spectroscopy (AA)

The specimen was dissolved by nitric acid than diluted with deionizewater to 50 mL as the analytical solution for FAAS. By FAAS, the lowestcobalt concentration can be detected (limit of quantitation, LOQ) is 1ppm; the concentration depart from linearity (limit of linearity, LOL)is 5 ppm. If the cobalt concentration of solution was out of applicablerange (1-5 ppm), solution will be properly diluted or concentrated andthe measurement was repeated. The Co concentration of the solution canbe calculated from its absorption referring to the calibration curve.The mass of cobalt WCo in the specimen can be obtained by solutionconcentration and volume.

Calculation of the mass of Sm (W₅₁,) and current efficiency (CE): Themass of Sm in the specimen Wsm can be calculated by:

$\begin{matrix}{W_{Sm} = {W_{Co}\frac{{Sm}\left( {{wt}\%} \right)}{{Co}\left( {{wt}\%} \right)}}} & \left( {{Equation}\mspace{20mu} 4} \right)\end{matrix}$

where Wco was obtained by AA and the Sm and Co content were from EDS.

Calculation of the current efficiency (CE): The current efficiency (CE)can be calculated by the charge used to obtain metal (Sm and Co) dividedby the charge (50 coulombs) passes during the electrodeposition. Thecharge used to obtain Sm and Co can be calculated by:

$\begin{matrix}{{C = {{C_{Co} + C_{Sm}} = {F\left( {\frac{W_{Co}Z_{{Co}^{2 +}}}{M_{Co}} + \frac{W_{Sm}Z_{{Sm}^{3 +}}}{M_{Sm}}} \right)}}}\left( {{unit}:{coulomb}} \right)} & \left( {{Equation}\mspace{20mu} 5} \right)\end{matrix}$

where C is the charge used to obtain metal (Co and Sm); Z is the valanceof the metal ion (ZCO²⁺=2 and Zsm=3); F is Faraday's constant, thecharge carried by a mole of electrons=96,500 C/mol; M is the atomic mass(M_(Co)=58.93 g and M_(Sm)=150.36 g); W is the mass of elements in thespecimen. The calculation of CE assumed the Sm and Co in deposit wereobtained from charge transfer reactions (the reduction of Co²⁺ and Sm³⁺)rather than chemical reactions (the precipitation of Co(OH)₂ andSm(OH)₂). The electrons passed during the electrodeposition were usedonly on the reduction of Sm, Co and H₂. This experimental assumptionprovided a first approximation of CE in Co—Sm electrodeposition.

g. Scanning Electron Microscopy (SEM)

SEM provides specimen surface images by collecting the secondary or backscattering electrons emitted from specimen after the electronbombardment [P. J. Goodhew, J. Humphreys and R. Beanland, Electronmicroscopy and analysis (3rd edition), Taylor & Francis, (2001), pp.196-205]. These images were used to study the topography, morphology andmicrostructure of electrodeposited Co—Sm alloys obtained from differentsolution and operating conditions.

h. Vibrating Sample Magnetometer (VSM)

VSM [D. Jiles, Introduction to magnetism and magnetic materials, Chapman& Hall, New York, (1991), pp. 47-53], a gradiometer measuring themagnetic induction difference with/without the specimen, gives a directmeasurement of the magnetization (M) under applied magnetic field (H). Aschematic of a typical VSM is shown in FIG. 62.

The disk shaped specimen was placed on a quartz sample holder and wasvibrated with fixed frequency in C-C′ direction. The magnetic field wasapplied parallel (A-A′ direction) and perpendicular (B-B′ direction) tofilm plane to obtain in-plane and perpendicular magnetic properties,respectively. The magnetic field swept between ″10,000 and 10,000 Oe wasused to obtain the hysteresis loop shown in FIG. 63.

Important magnetic properties of electrodeposited Co—Sm alloys can beobtained from its hysteresis loop as follows: He (Coercivity): themagnetic field needed to reduce the magnetic induction to zero after thematerial has been saturated (fully magnetized). Ms (SaturationMagnetization): maximum magnetization obtained in the hysteresis loop.Mr (Remanence): magnetization at applied magnetic filed equals to zero.Squareness (or the reduced remance): Mr/Ms. BHmax (Maximum EnergyProduct): the energy required to demagnetize a permanent magnet.

i. Effect of CD and Solution Temperature

Alloy Composition: Samarium deposit content (at %) increased withincreasing current density (CD). CD_(max) (the highest CD to obtainmetallic deposits) was extended by elevated solution temperatures (FIG.64( a)). At 25° C., CD_(max) was limited to 50 mA/cm² (Sm=14.5 at %),whereas for a solution temperature of 60° C., CD_(max) increased to 500mA/cm², resulting in deposit Sm content of 32.1 at %. Depending on CDand solution temperature, deposits of Sm content between 0 and 32 at %could be obtained from bath 1 (1 M Sm sulfamate, 0.05M Co sulfate, 0.15Mglycine) which satisfies the stoichiometric compositions ofintermetallic Sm₂Co₁₇ (10.5 at %) and SmCo₅ (16.7 at %) and, inaddition, Sm₂Co₇ (22.2 at %) and SmCo₃ (25 at %). Therefore, Co—Smalloys of sufficient Sm content for Sm—Co magnets (i.e. Sm₂Co₁₇ andSmCo₅) can be produced by electrodeposition.

Current efficiency (CE) calculated from the charge needed to obtainmetals (i.e. Sm and Co) divided by the total charge passed inelectrodeposition (50 coulombs). CE dropped sharply between 2 mA/cm²(66%) and 100 mA/cm² (20%) with little change between 100 mA/cm² and 500mA/cm² in the 60° C. solution, whereas the CE decreased almostexponentially in the 25° C. electrolyte, as shown in FIG. 64( b). CEswere higher at elevated solution temperatures.

To show individual changes in reduced products in electrodepositions, anomialized charge plot is provided in FIG. 65. Normalized charge orcharge ratio indicates the electroreduction of a specified species.Calculation of normalized charges was based on two assumptions. First,all electrons supplied to the cathode contributed to the production ofSm, Co and H₂ only; reduction of glycine or other species were ignored.Second, Sm and Co in deposits were obtained by electroreduction ofreactants (ions) at the cathode.

Precipitates of Sm(OH)₃ and Co(OH)₂ were not considered. Normalizedcharges of Sm and Co were calculated from charges required to obtain therespective metals in the deposits divided by the total charge passed (50coulombs). Normalized charge of H₂ was obtained by difference(subtracting charges to produce Sm and Co from the total charge).

From the variation of normalized charges with CD, as shown in FIG. 7, at60° C., increased CD (from 2 to 500 mA/cm²) resulted in a sharp increasein Sm from 0.01 to 0.09 and a decrease in Co from 0.65 to 0.13 leadingto a substantial increase in Sm deposit content from 1.3 to 32.1 at %(FIG. 64( a)). At 25° C., increased Sm deposit content from 3 to 15 at %with increasing CD from 2 to 50 mA/cm² was due to a sharp decrease in Co(normalized charge from 0.5 to 0.07) and a slight change in Sm from 0.02to 0.03.

The cathode potential was measured at various CDs and solutiontemperatures with a saturated calomel electrode (SCE) serving as thereference electrode. In alloy electrodeposition, the cathode potentialcan affect the composition of deposits [N. Ibl, Surf Tech., 10, 81,(1980)]. In addition, the cathode potential may change the nucleationrate (grain size) [M. Paunovic and M. Schlesinger, Fundamentals ofelectrochemical deposition, John Wiley & Son, Inc., New York, (1998),pp. 107-121], microstructures [H. Seiter, H. Fischer, and L. Albert.Electrochim. Acta, 2, 97 (1960)], and phases and orientation [N. A.Pangarov, J. Electroanal. Chem., 9, 70, (1965); N. A. Pangarov and S. D.Vitkova, Electrochim. Acta, 11, 1733, (1966)] of deposits. Thesecharacteristics govern magnetic properties of deposits. FIG. 66( a)shows the polarization curves of Co—Sm electrodeposition from bath 1 atvarious solution temperatures.

Lower solution temperatures resulted in more negative cathode potentialsin the electrodeposition of Co—Sm alloys. The dependence of Sm depositcontent on cathode potentials is shown in FIG. 66( b). A higher Smcontent was obtained at more negative cathode potentials. A linearrelationship was found between Sm deposit content and the cathodepotential, combining the effects of CD and solution temperatures.

It should be noted that the co-deposition of Sm and Co was observed atcathode potentials much less negative than the equilibrium potential ofSm (E°Sm/Sm²⁺=−2.65 V vs SCE) [W. M. Latimer, The oxidation states ofthe elements and their potentials in aqueous solution, Prentice Hall,N.Y., (1953), p 289]. This result indicates the co-deposition mechanismis more complex than the direct electrodeposition of both Co and Sm fromtheir respective aqueous ionic forms.

j. Crystal Structure

The dependence of crystal structures on CD and solution temperature wasdetermined by XRD. FIG. 67 and FIG. 68 show XRD results of depositsobtained from bath 1 at various CDs and at 25 and 60° C., respectively.It is noted that increased CD resulted in deposits changing fromcrystalline (or semi-crystalline) to non-crystalline; no diffractionpeaks of Co, Sm or Co—Sm intermetallics were found between 10 and 50mA/cm² at 25° C. and Sm or Co—Sm intermetallics between 2 and 500 mA/cm²at 60° C.; Co peaks disappeared at 60° C. and 500 mA/cm². Crystalstructures of electrodeposited Co—Sm crystallites were dominated by α-Co(hcp) phases; neither β-Co (fcc) nor Sm (rhombohedral) phases were foundin deposits.

At 25° C. (FIG. 67), (10.0), (00.2), (10.1) and (11.0) peaks of α-Co andvery weak (20.1) peak of SmCo₅ (hexagonal) and (20.2) peak of Sm₂Co₁₇(hexagonal) were observed at 2 mA/cm² (Sm=3 at %). In addition, weak(11.0) peaks of Sm(OH)₃ were found in the deposits at 25° C., but not at60° C. (see FIG. 68).

At 60° C. (FIG. 68), a strong (00.2) peak of a-Co was observed at 2mA/cm² decreasing with further increased CD at 10 and 25 mA/cm². Mixedorientations of (10.1), (11.0) and (10.0) peaks appeared from 10 (Sm 2.3at %) to 100 mA/cm² (Sm=9.2 at %). The (00.2) peak disappeared at 50mA/cm². Crystalline peaks were not seen at 500 mA/cm² (Sm=32.1 at %).

Effect of solution temperature on deposit crystal structures at variousCDs (2, 25 and 50 mA/cm²) are compared in FIG. 69. At higher CDs (25 and50 mA/cm²), decreased solution temperatures changed deposits fromcrystalline to non-crystalline structures, similar to the effect of theincrease of CD on deposit crystal structures (see FIG. 68 & FIG. 69). Atlow CD (2 mA/cm²), the decrease of solution temperature from 60 (Sm=1.3at %) to 25° C. (Sm=3 at %) resulted in the decrease of α-Co (00.2) peakintensity, and other a-Co orientations (i.e. (11.0), (10.0) and (10.1))were observed at 25 and 40° C. These orientations were also seen at 60°C., and both 10 and 25 mA/cm² (FIG. 68).

According to these XRD results, the change in deposit orientation followthe same trend as varying CD or solution temperature and are related toSm deposit content (or cathode potential). Thus, XRD results areorganized by dependence of cc-Co orientation on Sm deposit content atvarious CDs and solution temperatures in Table 21. Higher solutiontemperatures required higher Sm content to produce non-crystallinedeposits.

TABLE 21 Dependence of XRD patterns on Sm deposit content at various CDsand solution Deposit Current Density (mA/cm²) T (° C.) Properties 2 1025 50 100 200 300 500 550 60 hcp peaks (00.2) s (00.2) m (00.2) w (10.1)w (10.1) w (11.0) w (10.0) w non- non- (10.1) w (10.1) m (11.0) w (11.0)w (10.0) m crystalline metallic (11.0) m (11.0) w (10.0) m (10.0) m(10.0) m (10.0) m Sm (at %) 1.3 2.3 5.4 7.4 9.2 11.2 16.7 32.1 40 hcppeaks (00.2) m (00.2) w (11.0) w (10.0) w non- non- non-metallic (10.1)w (10.1) w (10.0) w crystalline crystalline (11.0) m (11.0) w (10.0) m(10.0) w Sm (at %) 1.3 6.2 7.7 8.3 13.0  18.2 25 hcp peaks (00.2) w non-non- non- non-metallic (10.1) w crystalline crystalline crystalline(11.0) s (10.0) s Sm (at %) 3.0 6.5 9.5 14.5  weak Sm(OH)₃ (10-50 mA/cm²at 25° C.), Sm₂Co₁₇ and SmCo₃ (2 mA/cm² at 60° C.) peaks were notincluded s, m and w compared the intensity of peaks, “s” = strong, “m” =medium, “w” = weak non-crystalline defined as no a-Co peaks was found inXRD

As shown in FIG. 66( b), Sm deposit content can be correlated to thecathode potential. Therefore, it is important to analyze the change inorientation with cathode potential. According to Pangarov's calculationfor hcp lattice [N. A. Pangarov, J. Electroanal. Chem., 9, 70, (1965)]in electrodeposition, an [00.1] orientation should be expected at verylow overpotentials, and with increase in overpotential, the followingorientation should appear: [10.1], [11.0], [10.0] and [11.2]. Later on,the experimental results [N. A. Pangarov and S. D. Vitkova, Electrochim.Acta, 11, 1733, (1966)] of electrodeposited Co (sulfate bath, pH5, 1580°C., 10-200 mA/cm²) were provided. Electrodeposited Co obtained at lowoverpotential (high solution temperatures and low CDs) resulted in apure [00.1] orientation. Medium overpotential (at low solutiontemperatures) leads to [11.0] and [10.0] as a mixed orientation. Highoverpotential, low solution temperatures and high CDs, had [10.0]orientation; [10.1] orientation was included with other orientation.

The dependence of orientation of electrodeposited Co—Sm alloys issimilar to electrodeposited hcp Co as strongly related to CD, solutiontemperature, Sm content (or cathode potential) in agreement withPangarov's calculation of the hcp lattice and his experimental resultsof hcp Co deposition.

k. Distortion of HCP Lattice

For more carefully studying the XRD patterns obtained at 60° C. frombath 1, Bragg angles (2ΘB of hcp-Co (00.2) and (10.0) peaks were foundvarying with Sm deposit content (FIG. 119). Increased Sm depositconstant resulted in the decrease of Bragg angle of (00.2) plane from44.425° (point c) to 44.179° (point d) for Sm content increased from 1.3to 2.3 at %. On the other hand, Bragg angle of (10.0) plane increasedfrom 41.643° (point a) to 41.798° (point b) for Sm content increasedfrom 2.3 to 16.7 at %.

Lattice constants of these deposits were calculated and compared to pureCo in Table 22. After comparing lattice constants of deposits ofdifferent Sm content, it was observed that lattice constant a (parallelto the basal plane of hcp structure) decreased with increased Sm depositcontent, whereas lattice constant c (perpendicular to the basal plane ofhcp structure) increased. Changed lattice constants implied thedistortion of hcp Co lattice by adding Sm atoms into Co matrix. Theradii of Co and Sm atoms are quite different; the atomic radius of Co is1.25 A and Sm is 1.81 A [J. P. Schaffer, A. Saxena, S. D. Antolovich, T.H. Sanders, S. B. Warner, The science and design of engineeringmaterials, McGraw-Hill Componies, Inc, New York, (1999), p 773 ^(I)°Centre d'information du cobalt, Cobalt monograph, 35, Rue Des Colonies,Brussels, Belgium, (1960), p75]. The size misfit

$\frac{R_{Sm} - R_{Co}}{R_{Co}} = {45\%}$

between Sm and Co could cause Co lattice distortion by adding Sm atoms.The distortion caused by addition of Sm tended to elongate Co latticealong the c-axis and compress along the basal plane. Furthermore, such adistortion of Co lattice may generate internal stress leading tomicrocracks in deposits. This will be discussed in the next section.

TABLE 22 Dependence of Bragg's angles (219) of (10.0) and (00.2) planesand lattice constants of electrodeposited Co-Stn alloys on Sm depositcontent Bragg's Angle (2⊖_(B)) Lattice Constant CD Sm Content (deg.) (Å)(mA/cm²) (at %) (10.0) (00.2) a c — Pure Co  41.595*  44.528*  2.507¹⁰ 4.069¹⁰  2 1.3 41.643 44.425 2.504 4.078  10 2.3 — 44.179 — 4.100  507.4 41.686 — 2.502 — 300 16.7 41.798 — 2.495 — *Bragg angles of pure Co(hep) (10.0) and (00.2) peaks were calculated from the lattice constantsof pure Co¹⁰ by Bragg's law (1) and the relationship between latticeconstants and interplanar spacing of (hkl) plane of hep structure (2)$\begin{matrix}{{2d_{hkl}\sin \; \theta_{B}} = {\lambda \mspace{14mu} (1)}} \\{\frac{1}{\left( d_{hkl} \right)^{2}} = {{\frac{4}{3}\left( \frac{h^{2} + {hk} + k^{2}}{a^{2}} \right)} + {\frac{l^{2}}{c^{2}}\mspace{14mu} (2)\quad}}}\end{matrix}\quad$ where λ (CuK_(α)) = 1.54184Å⊖_(e): Bragg's angle of(hkl) planed_(hkl): interplanar spacing of (hkl) plane

1. Morphologies and Microstructures

SEM pictures in FIG. 70 and FIG. 71 show the dependence of morphologyand microstructure on CD at 25 and 60° C., respectively. FIG. 72 andFIG. 73 compare the effect of solution temperature at 25 and 50 mA/cm²,respectively. The increase in Sm content due to increased CD (FIG. 70 &FIG. 71) or decreased solution temperature (FIG. 72 & FIG. 73) resultedin more microcracks and smaller particle sizes.

Microstructures of crystalline deposits were fiber-shaped nano-rods.With increased Sm content, deposits changed to non-crystallinestructures (XRD results) consisting of tiny roundish particles.

Microstructures of crystalline deposits of Co—Sm alloys are similar toelectrodeposited Co. According to Cavallotti et al [P. L. Cavallotti, E.Galbiati and T. Chen, in Electroplating Engineering and waste Recycle,D. D. Snyder, U. Landau, R. Sard (Eds.), ECS Pub., Pennington, N.J.,130, (1983)], celluar electrodeposited Co was obtained from pH 6.5sulfamate or sulfate solutions and changed to dendritic growth byincreasing CD. Outgrowing basal planes with “needle-shaped crystallineparticles” were found in deposits at 100 mA/cm² and 50° C. In addition,they found that the crystallite size was mainly influenced by CD andsolution temperature [P. L. Cavallotti, E. Galbiati and T. Chen, inElectroplating Engineering and waste Recycle, D. D. Snyder, U. Landau,R. Sard (Eds.), ECS Pub., Pennington, N.J., 130, (1983)]. Increasingsolution temperature increased grain size from tens of nanometers toseveral hundred nanometers. Increasing CD, the grain size decreased.Similar results of the change in grain size with CD and solutiontemperature were observed in electrodeposited Co—Sm alloys.

Particle size changed with CD, solution temperature and Sm contents.Particle size was measured and presented in Table 23 and FIG. 74. Theresults provided average values of particle size to illustrate thetendency rather than exact values at operating conditions. Because mostof the deposit microstructures were fiber-shaped nano-rods lying on thefilm plane, their lengths were much larger than widths and heights andwere measured individually. Particle lengths (σ_(L)) and widths (σ_(W))in the in-plane direction were determined by SEM; seven particles weresampled and measured from a SEM picture under an operating condition,and an average of particle size in the in-plane direction (σ_(∥)) wasthe arithmetic average of the particle length and width. Particlethickness (σ_(⊥)) (perpendicular to film plane) was calculated by theScherrer's equation according to FWHM of α-Co (10.0) peaks in XRDpatterns and represent the particle size in the perpendicular direction.

TABLE 23 Dependence of particle site on Sm deposit content at variousCDs and solution temperatures T Current Density (mA/cm²) (° C.) ParticleSize (nm) 25 50 100 300 500 60 Length σ_(L) 575 500 450 300 63 Widthσ_(W) 25 20 18 13 14 σ_(||) = (σ_(L) + σ_(W))/2 300 260 234 158 38Thickness, σ_(⊥) 22 18 15 10 — Sm (at %) 5.4 7.4 9.2 16.7 32.1 CrystalStructure crystalline non- crystalline 40 Length σ_(L) 440 205 95non-metallic Width σ_(W) 22 18 16 σ_(||) = (σ_(L) + σ_(W))/2 231 111 55Thickness, σ_(⊥) 20 17 — Sm (at %) 7.7 8.3 13.0 Crystal Structurecrystalline non- crystalline 25 Length σ_(L) 80 60 non-metallic Widthσ_(W) 18 13 σ_(||) = (σ_(L) + σ_(W))/2 49 37 Thickness, σ_(⊥) — — Sm (at%) 9.5 14.5 Crystal Structure non-crystalline Length σ_(L) and widthσ_(W) of particles (in-plane direction) are measured by SEM Thickness,σ_(⊥) of particles (perpendicular direction) are calculated byScherrer's equation according to α-Co (10.0) peaks in XRD — means noα-Co (10.0) peaks found in XRD pattern non-crystalline deposit)

Increased Sm deposit content leads to decrease in particle size, and thechange was more significant in the in-plane direction mainly due to thereduction of the particle length. For deposits of similar Sm content,higher solution temperatures resulted in larger particle sizes in thein-plane direction (σ_(∥)), whereas particle size in the perpendiculardirection (σ_(⊥)) varied little with solution temperature. From the viewpoint of nucleation and growth theory of electrocrystallisation, highercurrent density resulted in a higher nucleation rate [J. C. Puippe andF. Leaman, Theory and practice of pulse plating, American electroplatersand surface finishers society, Orlando, Fla., (1986), pp. 17-39]reducing the average distance between crystallites, therefore, adecrease in particle size can be expected.

m. Magnetic Properties

The most important characteristics governing the quality ofelectrodeposited hard magnetic films (i.e. coercivity Hc, saturationmagnetization Ms and squareness Mr/Ms) are grain size, crystal structureand orientation and the presence of alloying elements [L. T. Romankiwand D. A. Thompson, in Magnetic properties of plated films in Propertiesof Electrodeposits: Their Measurements and Significance, ElectrochemicalSociety, Princeton, N.J. (1975), pp 389-426]. Magnetic hysteresis loopsof deposits obtained at various CDs and solution temperatures weremeasured by VSM for an applied magnetic field scanning between −10K and10K Oe. In-plane (μ) and perpendicular (⊥) measurements represent themagnetic field applied parallel and perpendicular to the film plane,respectively. Magnetic properties of Hc, Ms and squareness were obtainedfrom hysteresis loops.

FIG. 75 gives examples of hysteresis loops obtained at 25 and 60° C. andat various CDs. It was noted that magnetizations (Ms) were easier in thein-plane direction than the perpendicular direction indicating theeasy-axis (EA) along the in-plane direction and the hard axis (HA) alongthe perpendicular direction. At 25 and 60° C., Ms_(∥) were higher thanMs_(⊥), and they approached each other sooner as magnetic fieldincreased. Ms_(∥) is used for the following discussion regardingapproaching magnetization saturation. On the other hand, Hc⊥ were higherthan Hc_(∥), and they got closer to each other as CD increased. At 25and 60° C., Ms and Hc⊥ decreased as CD increased. At constant CD, Ms andHe increased as solution temperature increased from 25 to 60° C. Theseresults can be correlated to the alloy compositions and crystalstructures of deposits. When deposits changed from crystalline tonon-crystalline structures with increased Sm content by increased CD,magnetic properties of deposits appeared more isotropic where the Ms⊥were closer to Ms_(∥) and the Hc⊥ were closer to Hc_(∥) Ms and Hc⊥decreased with increased Sm deposit content. The dependence of Ms and Heon alloy composition and deposit crystal structure were observed inthese hysteresis loops.

To further quantify the dependence of magnetic properties on alloycomposition and deposit characteristics, particle size, crystalstructures, Hc, Ms, and squareness of deposits were correlated to Smcontent in FIG. 76.

For the electrodeposited Co—Sm alloys before heat treatment, depositcharacteristics (crystal structure and grain size) were stronglydependent on Sm deposit content. With increase in Sm deposit content,deposits changed from hcp Co crystallites to non-crystalline structure,and grain size decreased as shown in FIG. 76( a). Ms depended on alloycomposition. Ms decreased linearly with increased Sm deposit content andwas in agreement with sputtered films” (FIG. 76( b)). He sharply butchanged little in the in-plane direction by increase in Sm content;He_(t) approached Hc_(∥) when deposits were of a non-crystallinestructure (FIG. 76( c)). At 60° C., dependence of coercivities on Smdeposit content (FIG. 76( c)) can be correlated to crystal structure andparticle size (FIG. 76( a)). Deposits obtained at 25 and 40° C. alsofollowed the same trend, see FIG. 74.

Hoffman has shown that the coercivity of ferromagnetic thin filmsdepends on crystallite size [H. Hoffman, IEEE Trans. Magnetics, 9, 17,(1973). Smaller crystallites result in decrease in coercivity. Hisprediction was later confirmed by the experimental results ofelectrodeposited Co films by Armyanov et al. [S. A. Armyanov and S. D.Vitkova, Phys. Status Solidi A, 26, 553, (1974)],[S. A. Armyanov and S.D. Vitkova, Surf Tech., 7, 319, (1978)] who found that coercivityincreased with particle size between 20 and 400 nm. For electrodepositedCo—Sm alloys, the in-plane particle size ((σ_(∥)=(σ_(L)+σ_(w))/2) werelarger than the perpendicular particle size (σ⊥) (FIG. 76( a)) becauseof fiber-shaped microstructures lying on the film plane (FIGS. 71( c),(f), (i) & (1)). For a fiber-shaped nano-rod lying on the film planealong the in-plane magnetic field (FIG. 77( b)), should consider theaverage particle size intersected by the in-plane magnetization,(σ⊥+σ_(w))/2≈σ_(∥). Hc⊥ should consider the average particle sizeintersected by perpendicular magnetic field, (σ_(L)+σ_(w))/2=σ_(∥). Forthose fiber-shaped nano-rods lying on the film plane but not along thein-plane magnetic field, the average particle sizes intersected byin-plane magnetization are between (σ⊥+σ_(w))/2 and (σ⊥+σ_(L))/²depending on the angle between the fiber axis and in-plane magneticfield.

The sharp reduction in Hci with increased Sm content (FIG. 76( c)) canbe correlated to the significant decrease in σ_(∥) (FIG. 76( a)). On theother hand, σ⊥ decreased little by increased Sm content resulting in asmall change in Hc_(∥). Larger σ_(∥) than σ⊥ could explain higher Hc⊥than Hc_(∥) of these deposits. When deposits became non-crystallineconsisting of tiny roundish particles (FIG. 70( i) and FIG. 71( o)), Hc⊥was closer to Hc_(∥) because of similar σ_(∥) and σ⊥ values. Thecoercivity of electrodeposited Co—P alloys and Co metal also depend oncrystal structure of deposits [K. Miller, M. Sydow and G. Dietz, Magn.Magn. Mater., 53, 269, (1985)]; increasing P content leads to a changefrom crystalline to non-crystalline deposits, and coercivity decreasedsignificantly. For electrodeposited Co—Sm alloys, increased Sm contentalso resulted in deposits changing from crystalline to non-crystalline(FIG. 76( a)). This can cause the decreased coercivities.

The squareness ratio (Mr/Ms) of deposits provides the preference ofmagnetization direction. For example, magnetization direction is closerto the in-plane direction when in-plane squareness is higher. Forferromagnetic materials, the magnetization direction strongly depends onthe minimization of the total magnetic energy. In the absence of anexternal magnetic field, magnetization direction is mainly controlled bythe magnetocrystalline anisotropy energy [R. C. O'Handley, Modernmagnetic materials, John Wiley & Son, Inc., New York, (2000), pp.179-215] and demagnetization energy [R. L. Comstock, Introduction tomagnetism and magnetic recording, John Wiley & Son, Inc., New York,(1999), pp. 24-28]. Minimization of magnetocrystalline anisotropy energyprefers to align magnetization along certain crystallographicdirections. In hcp crystals, the magnetization direction prefers toalign in the [00.1] direction [R. C. O'Handley, Modern magneticmaterials, John Wiley & Son, Inc., New York, (2000), pp. 179-215]. Tominimize demagnetization energy, magnetization prefers to lie along thelong axis of a particle because demagnetization energy is proportionalto the demagnetization factor which has the smallest value in the longaxis direction of a particle [R. L. Comstock, Introduction to magnetismand magnetic recording, John Wiley & Son, Inc., New York, (1999), pp.24-28]. For example, in a long cylinder particle, demagnetization factoralong this axis is zero and perpendicular to the axis is 0.5.

As discussed in the previous section, fiber-shaped nano-rods were foundto lie on deposit surfaces (long axis of particle aligned along thein-plane direction); particle size in the in-plane direction is largerthan the perpendicular. Higher in-plane squareness than perpendicularcan be explained by the alignment of magnetization direction (in absenceof external field) along the long axis of particles to minimizedemagnetization energy. On the other hand, the effect ofmagnetocrystalline anisotropy energy was not significant. (00.2) peakswere observed (see Table 21: 25° C.: 2 mA/cm², 40° C.: 2 and 10 mA/cm²,60° C.: 2, 10 and 25 mA/cm²) indicating the [00.1] orientation was alongthe perpendicular direction in these deposits. However, magnetizationdid not align along the perpendicular direction and resulted in higherperpendicular squareness.

Compared to the squareness of crystalline and non-crystalline sputteredSmCos deposits, crystalline deposits have higher squareness (0.3-0.8)than non-crystalline (−0.2) [C. Prados and G. C. I ladjipanayis. J.Appl. Phys., 83, 6253, (1998)]. Deposits changed from crystalline tonon-crystalline structure (FIG. 76( a)) by increased Sm contentindicating reduction in squareness. Magnetic properties ofnon-crystalline deposits exhibit isotropic over anisotropic (easy andhard axis caused by crystallographic structures no longer exist).Therefore, Hc_(∥) and Hc⊥ (FIG. 76( c)) of a non-crystalline Co—Smdeposit were quite close. The in-plane and perpendicular Ms were alsocloser when deposits were non-crystalline (see FIG. 75( c), 25° C. orFIG. 75( i), 60° C.). On the other hand, the in-plane squareness wasstill higher than perpendicular (FIG. 76( d)) probably because thedemagnetization direction is still aligned along the in-plane directionfor the reduction of demagnetization energy. For non-crystallinedeposits, particle size in the in-plane direction is still larger thanin the perpendicular direction (see Table 21 and FIG. 74).

n. Effect of Solution pH

Alloy Composition: Solutions of various pHs were adjusted from bath 1 bysulfamic acid to study the effect of solution pH on Sm content andcurrent efficiency as shown in FIG. 78.

For solution pH between 2 and 6, increased CD or decreased solutiontemperature resulted in higher Sm deposit content. At low CDs (10 & 50mA/cm²) and 25° C., increasing solution pH increased Sm deposit contentand then reached a constant. At 60° C., Sm content increased withincreased solution pH and at 100 and 300 mA/cm², Sm content reachedmaxima at pH 5 and 4. It is also important to point out that increasingCD results in increased rate of water reduction leading to increase inpH at cathode surface. The pH at the cathode surface is affected by bothCD and solution pH. The results in FIG. 78( a), however, a plot of Smcontent and solution pH. Estimation of the pH at the cathode surface maybe made by calculation.

According to the mechanism proposed by Schwartz et al [M. Schwartz, N.V. Myung, and K. Nobe, J. Electrochem. Soc., 151, C468, (2004)], aheterodinuclear complex containing Sm and Co ions and glycine resultedin the co-deposition of Sm with Co. It is known that the glycinestructure depends on solution pH and is considered as cationic(⁺H₃N—CH₂COOH ) at low pH, dipolar (⁺H₃N —CH₂COO⁻) at medium pH (˜6) andanionic (H₂N—CH₂COO⁻) at higher pH; glycine structures at different pHmight alter its complexing ability with Sm and Co ions and change theco-deposition rate or Sm and Co.

Higher CEs were obtained at lower CDs and higher solution temperaturesat various solution pH (FIG. 78( b)). CE varied little with solution pHcompared to CD and solution temperature (FIG. D6(b)).

o. Crystal Structure

In the previous section, it was observed that crystalstructuress ofelectrodeposited CoSm alloys from bath 1 (1M Sm sulfamate, 0.05M Cosulfate, 0.15M glycine, pH 6) were dominated by a-Co (hcp) with someSmCos and Sm₂Co₁₇ crystallites. Weak Sm(OH)₃ (11.0) peaks were found indeposits obtained at 25° C., but not in deposits at 60° C. Twointeresting crystal structure problems were studied by varying the pH ofbath 1. First, can low pH solutions eliminate Sm(OH)₃ in deposits?Second, does the decreased pH result in the hcp→fcc transition which isoften found in electrodeposited Co at low pH? The second problem is notonly interesting in crystallography but also important for magneticproperties of deposits because magnetic properties of hcp and fcc Co arequite different. For example, hcp-Co has only one easy-axis [00.1] formagnetization, whereas fcc-Co has four easy axis of [111]. The energy ofmagnetocrystalline anisotropy of hcp-Co is higher than fcc-Co [Centred'information du cobalt, Cobalt monograph, Brussels, Belgium, (1960), pp95-100]. The Curie temperature of hcp-Co is 887° C. and fcc-Co is 1121°C.

XRD results of deposits obtained at various solution pHs and. CDs areshown in FIG. 79 and FIG. 80 (25° C.), and FIG. 81 to FIG. 84 (60° C.).These results are summarized in Table 24. Most deposits obtained at 25°C. (10 and 50 mA/cm²) were non-crystalline except for pH 2 at 10 mA/cm²containing (10.0) and (00.2) peaks of a-Co. Decreased solution pH didnot eliminate Sm(OH)₃; (11.0) peaks of Sm(OH)₃ were found in deposits at25° C. between pH 2 and 6. On the other hand, the Sm(OH)₃ peak was notobserved at 60° C. At 60° C. for different pHs, the change inorientation with increasing CDs were similar.

TABLE 24 Dependence of XRD patterns on Sm deposit content at various CDsand solution pH Solu- T tion Deposit Current Density (mA/cm²) (° C.) pHProperties 10 50 100 300 25 6 hcp peaks non-crystalline non-metallic Sm(at %) 2.3 7.4 5 hcp peaks non-crystalline non-metallic Sm (at %) 1.77.0 4 hcp peaks non-crystalline non-metallic Sm (at %) 1.7 3.1 3 hcppeaks non-crystalline non-metallic Sm (at %) 0.7 2.7 2 hcp peaks (00.2)m non- non-metallic (10.0) m crystalline Sm (at %) 0.5 1.5 60 6 hcppeaks (00.2) m (10.1) w (10.1) w (10.0) w (10.1) w (11.0) w (11.0) w(11.0) m (10.0) m (10.0) m (10.0) m Sm (at %) 2.3 7.4 9.2 16.7 5 hcppeaks (00.2) m (11.0) w (10.1) w non- (10.1) m (10.0) m (11.0) wcrystalline (11.0) m (10.0) w (10.0) s Sm (at %) 1.7 7.0 11.8  22.6 4hcp peaks (00.2) w (00.2) w (10.0) w non- (10.1) w (10.1) w crystalline(11.0) w (11.0) w (10.0) m (10.0) m Sm (at %) 1.7 3.1 10.8  28.1 3 hcppeaks (00.2) w (00.2) m (10.0) w (10.0) w (10.1) w (10.1) w (11.0) w(11.0) m (10.0) m (10.0) m Sm (at %) 0.7 2.7 8.5 24.2 2 hcp peaks (00.2)m (00.2) w (00.2) w non- (10.1) m (10.1) w (10.1) w crystalline (11.0) s(11.0) m (11.0) w (10.0) s (10.0) m (10.0) w Sm (at %) 0.5 1.5 0.9 18.9weak Sm(OH)₃ (10~50 mA/cm² at 25° C.), Sm₂Co₁₇ and SmCo₃ (2 mA/cm² at60° C.) peaks were not included s, m and w compared the intensity ofpeaks, “s” = strong, “m” = medium, “w” = weak non-crystalline defined asno α-Co peaks was found in XRD

Generally, the α-Co (hcp) phase is stable at temperature below 417° C.,and the {tilde over (β)}Co(fcc) phase is thermodynamically stable onlyabove 417° C. However, it was reported that both phases can be obtainedin electrodeposited Co with α-Co obtained at pH higher than 2.9 and β-Coat pH less than 2.4. (bath: Co sulfate, NaCl, 18° C., 12 mA/cm²) [J.Goddard and J. G. Wright, Brit. J. Appl. Phys., 15, 807, (1964)].Nakahara et al. [S. Nakahara and S. Mahajan, Electrochem. Soc., 127,283, (1980)] (bath: Co sulfate, NaCl and boric acid, 25° C., 10 mA/cm²)further proposed that the formation of metastable Co hydride at low pHcould be the reason for the formation of β-Co. High density inclusionsof Co(OH)₂ were observed in high pH (˜5.7) deposits [S. Nakahara and S.Mahajan, Electrochem. Soc., 127, 283, (1980)]. It was concluded that thesolution pH is the most important parameter governing the crystalstructure of electrodeposited Co where deposits at high pH results inα-Co and low pH generates β-Co [S. Nakahara and S. Mahajan, Electrochem.Soc., 127, 283, (1980)].

For Co—Sm deposits from bath 1, β-Co crystallites were not found fromsolution pH from 6 to 2 at 10 & 50 mA/cm² and 25° C. (FIG. 79 and FIG.80), and at 10-300 mA/cm² and 60° C. (FIG. 81 to FIG. 84)). Furthermore,inclusions of Co(OH)₂ was not observed even for deposits obtained at pH6. In Hull Cell studies, it was observed that in the absence of glycine,Co(OH)₂ and Sm₂O₃.CoO mixtures were found in deposits. It has beenreported that the Co-glycine complex can inhibit the formation ofCo(OH)₂ [C. F. Diven, F. Wang, A. M. Abukhdeir, W. Salah, B. T. Layden,C. F. Geraldes, and D. M. Freitas, Inorg. Chem., 42, 2774, (2003)]. Theappearance of glycine probably prevents inclusions of Co(OH)₂ bycomplexing with Co ions.

p. Morphologies and Microstructures

SEM pictures of deposits obtained at various solution pHs and CDs at 25°C. and 60° C. are shown in FIG. 65 and FIG. 66 and FIG. 67 and FIG. 590,respectively. Dependence of particle size on Sm deposit content atvarious pHs, temperatures and CDs is shown in FIG. 59.

At 25° C. (FIG. 85), there were more microcracks in deposits obtained athigher CDs or solution pHs. These changes resulted in high Sm depositcontents. At 60° C. (FIG. 87), microcracks were less significantcompared to 25° C. even for high Sm deposit contents. Forelectrodeposited Co-rich Co—Sm alloys (before the formation ofintermetallic compounds) the addition of Sm into the Co matrix probablyinduced internal stress by the misfit of lattice constants of Co and Sm.Further addition of Sm increased internal stress increasing microcracksin the deposits. Stacking faults and defects formed during theelectrodeposition also resulted in internal stress. Elevated solutiontemperatures resulted in adsorbed atoms of higher mobility on thecathode surface facilitating their reaching kink or terrace sites thatreduce defects and internal stress in deposits.

High magnitude (50,000×) SEM results at 25° C. show ridge-shapedmicrostructures were observed at pH 2 below Sm=3.1 at % (FIGS. 86( g) &(h)). Ridge-shaped microstructures were also observed in Co-rich Co-Fe²⁸and Ni—Co²⁹ alloys. At pH 4 and 10 mA/cm², tiny roundish particles mixedwith large plate-shaped particles resulted in a wider distribution ofparticle size (FIG. 86( d)).

At 60° C., microstructures at pH 2 were more compact (FIGS. 88( g) &(h)). At 50 mA/cm microstructures were large ridge-shaped (FIG. 88( h)).With decreased CD to 10 mA/cm², tiny protrusions embedded in theridge-shaped matrix had a two-phase structure (FIG. 88( g)). Fordeposits with similar Sm deposit contents obtained at different pH bathscould have quite different microstructure shapes and particle sizes (forexample, FIG. 88( d) vs. (h), FIG. 86( a) vs. (i)).

Vicenzo and Cavallotti studied the growth modes of electrodeposited Cofrom sulfamate baths. Different pH baths led to different morphologiesand microstructures. Three basic modes were identified as: outgrowth,lateral growth and cluster growth which were strongly dependent onsolution pH. Increased particle size was found as decreased [A. Vicenzo,P. L. Cavallotti. Electrochim. Acta, 49, 4079, (2004)]. In Co—Smelectrodeposition, deposit microctructure varied with solution pH.However, the dependence of particle size on solution pH was notsignificant.

At a fixed solution pH, increased CD or decreased solution temperaturegenerally brought about an increase in Sm deposit content leading to thereduction of particle size (FIG. 89). However, at pH 2 and 60° C.particle size increased by increasing CD from 10 to 50 mA/cm² (FIG. 88).The dependence of particle size at various pH on Sm deposit content wasmore scattered compared to a fixed pH (pH6, FIG. 74). Different shapesof microstructures obtained at different pH make this dependence morecomplex.

q. Magnetic Properties

FIG. 90 gives magnetic properties of deposits obtained at 25, 60° C. andat various solution pHs. Ms values were dependent on alloy compositionsbut not on solution pH. Ms decreased with increased Sm deposit contentand were in good agreement with sputtered deposits.

Similar to the results on the effect of CD and solution temperatures inFIG. 18( c), Hc_(∥) decreased with increased Sm deposit content (FIGS.90( c) & (d)) due to decreased (FIG. 89). Hc_(∥) varied little with Smdeposit content (FIGS. 90( c) & (d)) for small change in σ_(∥) withincreased Sm content (FIG. 89) (see FIG. 77).

In-plane squareness was higher than perpendicular due to the alignmentof magnetization direction along the in-plane direction to reduce thedemagnetization energy. Squareness decreased with increased Sm contentby the change from crystalline to noncrystalline structure.

r. Effect of Fluid Dynamics

Alloy Composition: The rotating disk electrode (RDE), which changes themass transfer rate of electrolyte from the bulk solution to the cathodesurface by varying the rotation rate, was used to study the effect offluid dynamics on Co—Sm alloy deposition. Because the brass substratewas placed facing down to the button of the cell, when the RDE wasstationary, hydrogen bubbles generated from water reduction accumulatedon the cathode surface resulting in burnt deposits with poor adhesion(films fell off the electrode after electrodeposition). For this reason,deposits obtained from parallel electrodes (without agitation) were usedin place of 0 rpm (deposits) in the following discussions to assess thedifference with/without agitation.

Deposit Sm content sharply decreased, then reached a constant byincrease in rotating rate (FIG. 91( a)). On the other hand, CE increasedwith increasing rotating rate (FIG. 91( b)). Agitation by RDE resultedin metallic deposits at 100 mA/cm² in contrast to deposits obtainedwithout agitation (parallel electrodes), but higher Sm deposit contentwere not obtained. Even though the concentration of Co ions (0.05M) wasmuch lower than Sm ions (1M) in bath 1, the deposition rate of Co wasmuch greater than Sm (FIG. 92). A higher rotating rate did notsignificantly increase the deposition rate of Sm; but enhancedsubstantially the deposition of Co and suppressed H₂ gas evolution. Thisindicates that the decrease in Sm deposit content by a greater agitationrate (FIG. 91( a)) was due to the increase in Co deposition rate (Smdeposition rate remained unchanged). These results indicate masstransfer effects in the co-deposition of Co.

As discussed in the previous section on parallel electrodes,, thedeposits were not metallic at 100mA/cm². White powder and burnt regionsappeared on deposit surfaces. These non-metallic regions were confirmedas mixtures of oxides and hydroxides in the Hull cell study. SEMpictures of the deposit at 100 mA/cm² (parallel electrodes, noagitation) are shown in FIGS. 93( a)-(c). High density microcracks werefound in the deposit (FIG. 93( a)) and the white powder had a porousmicrostructure (FIG. 93( c)). For deposits obtained with agitation (1000and 2000 rpm), metallic deposits were obtained and microcrack densitiesremained the same (comparing FIGS. 35( a), (d) & (e)) but the porousmicrostructure disappeared.

s. Magnetic Properties

The morphology and microstructure of the non-metallic deposit (confirmedas mixtures of hydroxides and oxides) obtained at 100 mA/m² by parallelelectrodes was compared to metallic deposits in the previous section.The appearance of oxide and hydroxide phases in this deposit also causedthe degradation of magnetic properties, such as Ms. Compared to tosputtered Co—Sm alloys with similar Sm content, this deposit (parallelelectrodes, 25° C., no agitation, 100 mA/cm, bath 1) had much lower Ms(about 30% f sputtered) (FIG. 94( a)).

Similar to the results of magnetic properties discussed in previoussections, Hc and squareness of deposits showed strong dependence on Smdeposit content. Perpendicular He decreased significantly but in-planeHc decreased little by increasing Sm deposit content. In addition, Hcwas higher in the perpendicular direction. In-plane squareness washigher than perpendicular squareness; squareness decreased more inin-plane direction than in the perpendicular direction with decreased Smdeposit content.

t. Effect of Sm Sulfamate

Alloy Composition: Baths containing 0.05M Co sulfate, 0.15M glycine andSm sulfamate varying from 0.25 to 1M were used to study the effect of Smsulfamate on deposit properties. The decrease of Sm sulfamateconcentration resulted in non-metallic deposits (Table 25). Whitepowders consisting of Sm(OH)₃ and Co(OH)₂ (XRD) appeared in depositsobtained for Sm sulfamate concentration <1M at 60° C. and low CDs (25 &50 mA/cm²). CD_(max) (the highest CD with metallic deposits) decreasedas Sm sulfamate concentration decreased (Table 25).

In general, decreased Sm sulfamate concentration increased Sm depositcontent (FIG. 95( a)). CE increased with decreased Sm sulfamateconcentration (FIG. 95( b)). The deposition rate of Sm and Co wasenhanced by decrease in Sm sulfamate concentration, whereas Hi evolutionwas suppressed (FIG. 96). However, by decrease in Sm sulfamateconcentrations, Sm(OH)₃ or Sm oxide was found in metallic appearingdeposits (Table 25) at 25° C. (FIG. 97 & FIG. 98) and 60° C. (FIG. 99 &FIG. 100). The precipitation of Sm(OH)₃ or Sm oxide in deposits maycontribute to the increase in Sm deposit content with decreased Smsulfamate concentrations.

TABLE 25 Deposit appearance obtained at various Sm sulfamateconcentrations, CDs and temperatures [Sm sulfamate] 1M 0.75M 0.5M 0.25M25° C. CD (mA/cm2)  25 M M M M  50 M M M b 100 b b b B 60° C. CD(mA/cm2)  25 M w w w  50 M m w w 100 M M M b 300 M M b B 500 M b B B

u. Crystal Structures

XRD results in the previous section show weak (11.0) peaks of Sm(OH)₃ indeposits obtained at 25° C. (FIG. 67). At 25° C. and 25 mA/cm², similarXRD patterns were found for deposits obtained from baths containingvarious Sm sulfamate concentrations (FIG. 97). On the other hand, at 50mA/cm² (25° C., FIG. 98), the intensity of Sm(OH)₃ (11.0) peaks becamestronger when Sm sulfamate concentrations were less than 0.75M.Meanwhile, Co(OH)₂ (11.0) peaks appeared for Sm sulfamate concentrationsless than 0.5M.

At 60° C., no hydroxide peaks were found in deposits from bath 1 (Smsulfamate=1M) (FIG. 68). However, Sm(OH)₃ (11.0) and Co(OH)₂ (11.0)peaks appeared for Sm sulfamate concentrations of 0.75M (60° C. and 50mA/cm²) or less with peak intensities increasing with decreasing Smsulfamate concentrations (FIG. 99). A (111) peak of SmO was observedwhen Sm sulfamate concentration reached 0.25M. With further increase ofCD to 100 mA/cm² (FIG. 100), peaks of CoO and SmCoO₃ were found.

Generally, decrease in Sm sulfamate concentrations resulted in morehydroxides (Sm(OH)₃ and Co(OH)₂), except for deposits obtained at 25° C.and 25 mA/cm². SmO, CoO and SmCoO₃ were observed at 60° C. and 100mA/cm² for Sm sulfamate concentrations of 0.5M and less. Co(OH)₂ and CoOwere not only found in non-metallic deposits but also in metallicdeposits (FIG. 98( b), FIG. 99( c) and FIG. 100( b)) degrading theirsaturation magnitization.

v. Magnetic Properties

Magnetic properties of deposits obtained at various Sm sulfamateconcentrations are shown in FIG. 101. Ms values of non-metallic depositswere ⅕ to ¼ that of sputtered deposits. Co(011)7 or CoO in thesenon-metallic deposits (FIG. 40( a) and FIG. 42( a)) degraded Ms byreducing the ferromagnetic phase (metallic Co) to non-ferromagneticphases (Co(OH)₂ or CoO). For metallic deposits containing Co(OH)₂ or CoOobtained at 25° C., 50 mA/cm², [Sm sulfamate]=0.5M (FIG. 40( b)) and at60° C., 100 mA/cm², [Sm sulfamate]=0.5M (FIG. 42( b)), Ms values werealso much lower than sputtered deposits.

Similar to previous observations (FIG. 76( c)), He depended on Smdeposit content. Higher Sm deposit content resulted in lower Hc (compareFIG. 101( e) with (a), (f) with (b)); the change in perpendicular Hc wasmore significant than in-plane Hc.

Squareness followed similar trends as discussed (FIG. 76( d)): in-planesquareness was higher than perpendicular, and squareness decreased withincreased Sm deposit content (compare FIG. 101( g) with (a), (h) with(b)).

w. Effect of Glycine

Alloy Composition: Baths consisting of 1M Sm sulfamate, 0.05M Co sulfateand glycine varied from 0.05 to 0,5M were used to study the effect ofglycine on deposit properties. Dependence of Sm content and currentefficiency on glycine is in FIG. 102.

At 25° C., low glycine concentrations resulted in non-metallic deposits.Metallic deposits were obtained when glycine concentration was higherthan 0.1M at 25 mA/cm² and 0.15 M at 50 mA/cm². For metallic depositsobtained at 25° C., Sm deposit content decreased with increasing glycineconcentration. At 60° C. and low CDs (25 and 50 mA/cm²), Sm depositcontent increased, reached a maximum and then decreased with glycineincreased from 0 to 0.5M; highest Sm contents were obtained at 0.15Mglycine. With further increase in CD to 300 mA/cm², the highest Smcontent was obtained at 0.1M glycine, and metallic deposits were notobserved at glycine concentration below 0.1M. Highest Sm contents wereobtained at glycine concentration between 0.1M (glycine: Co²⁺=2:1) and0.15M (glycine: Co²⁺=3:1). CE increased with increased glycineconcentration at 25° C., whereas had no significant dependence onglycine concentration at 60° C.

According to the mechanism proposed by Schwartz et al [M. Schwartz, N.V. Myung, and K. Nobe, J. Electrochem. Soc., 151, C468, (2004)], aheterodinuclear complex containing Sm and Co ions and glycine resultedin the co-deposition of Sm with Co. Different glycine to metal ionsratio may change the complex composition (i.e. types and concentrations)in solutions affecting the reduction of Sm and Co and resulting indifferent Sm deposit contents.

x. Crystal Structure and Microstructure

Addition of glycine prevents the precipitation of Co(OH)₂ and Sm(OH)₃ asshown in the Hull cell results. Formation of Co-glycine complex has beenreported to inhibit the formation of Co(OH)₂ in aqueous solutions³¹ andcould be the reason of preventing the precipitation of hydroxides indeposits. More studies by parallel electrode deposition will bediscussed in this section. At 25° C. weak Sm(OH)₃ (11.0) peaks werefound in deposits were found in deposits obtained from 0.15M glycinesolutions (FIG. 103( b) or FIG. 67). However, at 60° C. 0.15M glycineeffectively prevented the precipitation of hydroxides in deposits (FIG.104( b)).

On the other hand, deposits obtained at 0.05M and 0.5M glycineconcentrations had stronger Sm(OH)₃ (11.0) peaks compared to 0,15Mglycine (25° C.: FIG. 103, 60° C.: FIG. 104). Co(OH)₂ (11.0) peaks werealso found in these deposits (0.05 and 0.5M glycine). Adding too little(glycine: Co²⁺=1:1) or too much glycine (glycine: Co²⁺=10:1) to thesolution did not prevent the formation of hydroxides (Co(OH)₂ andSm(OH)₃).

y. Magnetic Properties

FIG. 105 shows the magnetic properties of deposits obtained at variousglycine concentrations. For metallic deposits obtained from thesolutions of glycine concentrations ranging from 0.05 to 0.5M had Msvalues comparable to sputtered deposits (FIGS. 105( c) & (d)). Even inthe presence of some hydroxides in deposits obtained at 0.05M and 0.5Mglycine (FIG. 103 and FIG. 104), significant degradation of Ms valueswere not observed compared to the deposits containing hydroxides andoxides obtained at low Sm sulfamate concentrations (see FIG. 101).

In-plane and perpendicular He for deposits obtained by varying glycineconcentrations did not change significantly (FIGS. 105( e)&(0), butperpendicular was greater than in-plane Hc. At 25 and 60° C., in-planesquareness was greater than perpendicular squareness.

z. Effect of NH₄ Sulfamate

Alloy Composition: Schwartz et al [M. Schwartz, N. V. Myung, and K.Nobe, J. Electrochem. Soc., 151, C468, (2004)] studied theelectrodeposition of Co—Sm alloys under agitation of the platingsolution containing 0.9M Sm sulfamate, 0.12M Co sulfamate, 0.36M glycineand 0.9M NH₄ sulfamate resulting in maximum Sm deposits of 8 at %.However, Hull cell results indicated that the presence of NH₄ sulfamatein solution reduced Sm deposit content. In the absence of NH₄ sulfamate(bath 1), a Sm deposit content of 26 at % was obtained at 60° C. and 650mA/cm² from an unagitated solution. A Sm deposit content of 32 at % wasobtained with parallel electrodes from bath 1 at 60° C. and 500 mA/cm²(unstirred).

Although addition of NH₄ sulfamate resulted in decreased Sm content, itwas of interest to study how NH₄ sulfamate reduced Sm deposit contentand affected deposit properties. Baths consisting of 1M Sm sulfamate,0.05M Co sulfate, 0.15M glycine and NH₄ sulfamate varied from 0 to 1Mwere used to study the effect of NH₄ sulfamate. Addition of NH₄sulfamate resulted in decreased Sm content (FIG. 48( a)) confirming theHull cell results. The decrease in Sm content was more substantial athigher CDs. CE increased with increased NH₄ sulfamate concentration at25° C. but varied little at 60° C. (FIG. 106( b)). Increased NH₄sulfamate concentration suppressed Sm deposition (FIG. 107( a)) andenhanced Co deposition (FIG. 107( b)) leading to decreased Sm content(FIG. 106( a)).

The heterodinuclear complex containing Sm and Co ions and glycine wasproposed resulting in the co-deposition of Sm with Co [M. Schwartz, N.V. Myung, and K. Nobe, J. Electrochem. Soc., 151, C468, (2004)].However, NH₃ from the deprotonated NH₄ ⁺ could compete with glycine toform other complexes with Co and Sm ions and result in changes incompositions of complexes in solution. This can decrease Sm depositcontent by suppressing co-deposition of Sm.

aa. Crystal Structure

FIG. 108 and FIG. 51 compared the crystal structures of depositsobtained from solution with (bath 1)/without 1M NH₄ sulfamate (bath 8)at 25 and 60° C., respectively.

At 25° C., non-crystalline deposits were obtained at CD over 10 mA/cm²for both baths with/without 1M NH₄ sulfamate. At 2 mA/cm², only the α-Co(00.2) peak was found in the presence of 1M NH₄ sulfamate (bath 8). Inits absence (bath 1), addition of α-Co (10.1), (11.0) and (10.0), SmCo₅(hexagonal) (20.1) and Sm₂Co₁₇ (hexagonal) (20.2) peaks were observed.It was interesting to note the absence of the Sm(OH)₃ peak in depositsfrom bath 8 for CD≧25 mA/cm². At 60° C. (FIG. 109), the dependence ofcrystal structure on CD for deposits from bath 8 was similar to bath 1,except no (10.1) peak was observed. Furthermore, unlike depositsobtained at 25° C., 60° C. deposits did not exhibit the Sm(OH)₃ peak.

bb. Morphologies and Microstructures

For deposits obtained at the same temperature and current density thepresence of NH₄ sulfamate resulted in much smaller microcracks indeposits than in its absence (FIG. 110). The former produced lower Smdeposit content leading to lower internal stressed deposits as discussedin the previous section.

Microstructures obtained from baths with/without 1M NH₄ sulfamate werequite similar, except at 60° C. and 50 mA/cm² (FIG. 111).

At 60° C. and 50 mA/cm², rigid-shaped rods and spherical particles wereobserved in deposits obtained from bath 8 (with 1M NH₄ sulfamate) (FIG.111( b)). These microstructures were more compact compared to depositsfrom bath 1 (without NH₄ sulfamate).

cc. Magnetic Properties

FIG. 112 shows the magnetic properties of deposits obtained from bathscontaining various NH₄ sulfamate concentrations. Deposits obtained fromsolutions with/without NH₄ sulfamate had similar Ms and were in accordwith the Ms of sputtered deposits (FIGS. 112( a) & (b)). For thedeposits (with NH₄ sulfamate), Hc⊥ was much greater than Hc_(∥) anddecreased significantly by increasing Sm deposit content, whereas Hc_(∥)varied little (FIGS. 112( c) & (d)). Both in-plane and perpendicularsquareness decreased with increase in Sm content and the formersignificantly larger. The dependence of He and squareness on Sm contentwas not affected by the presence of NH₄ sulfamate.

dd. Supporting Electrolytes

Alloy Composition: Addition of NH₄ sulfamate in solution was found tosuppress the deposition of Sm and enhance the deposition of Co resultingin decreased Sm content. As a supporting electrolyte, NH₄ sulfamatecould change or modify the glycinato-complex structure in solutionthereby affecting the deposition of Sm and Co.

Taube and Gould [H. Taube and E. S. Gould, Acc. Chem. Res., 2, 321,(1969)] indicated that NH₃ is not a good bridging ligand for electrontransfer in redox reactions, and a metal ion-NH₃ complex could result inlow reaction rates. Further, inclusion of Cl— ions could accelerateredox reactions and is referred as a good bridging ligand or mediatinggroup. Therefore, it was of interest to include the effect of bridgingligands on electrodeposition of Co—Sm alloys. Supporting electrolytes of1M NH₄ sulfamate, NH₄Cl or KCl were added to bath 1 to study theinfluence of NH₃ and Cl— bridging ligands on deposit composition andproperties.

The highest Sm content of metallic deposits obtained from these bathsranked as: 1M KCl (18 at % at 50 mA/cm²) >no supporting electrolyte(14.5 at % at 50 mA/cm²)>1M NH₄Cl (9.7 at % at 100 mA/cm²)>1M NH₄sulfamate (8.1 at % at 300 mA/cm²) from 25° C. solutions (FIG. 113( a)).Sm deposit content increased with the addition of Cl— and decreased withthe addition of NH₄ ⁺ (or NH₃). Addition of KCl did not increaseCD_(max). Compared to no supporting electrolyte (50 mA/cm²), however,the addition of NH₄Cl and NH₄ sulfamate resulted in increased CD_(max)to 100 and 300 mA/cm², respectively.

With increased solution temperatures (60° C.), addition of NH₄Cl or NH₄sulfamate both extended the CD_(max) to 900 mA/cm², whereas addition ofKCl limited the CD_(max) to 300 mA/cm² (FIG. 113( b)). The highest Smdeposit contents were: no supporting electrolyte (32 at % at 500mA/cm²)>NH₄Cl (27 at % at 900 mA/cm²) NH₄ sulfamate (27 at % at 900mA/cm²)>KCl (21 at % at 300 mA/cm²). Because of the lower limitingCD_(max) (300 mA/cm²), the highest Sm deposit content from theKCl-containing bath was not higher than deposits from NH₄Cl or NH₄sulfamate baths. However, with CDs<300 mA/cm², the Sm deposit contentranked: KCl>no supporting electrolyte NH₄Cl>NH₄ sulfamate, similar tothe deposits from 25° C. baths. The dependence of Sm content on NH₄ ⁺and Cl— ions (as bridging ligands) was observed; at a fixed CD, the Smcontents obtained from Cl— containing solutions were higher thanNH₄-containing solutions. CEs decreased with increasing CD at 25° C.;CDs at 60° C. decreased but reached a minimum at 300 mA/cm² and thenincreased slightly (FIG. 114).

At 25° C., Sm deposit content increased with increasing CD (FIG. 113(a)) mainly due to the decreased. Co deposition (FIG. 115( a)); thedecrease of Co deposition was sharper for solutions in the absence ofsupporting electrolyte. At 60° C., increasing CD increased Sm depositionand decreased Co deposition (FIG. 115( b)). At both 25 and 60° C., Smdeposition was enhanced by addition of Cl— ions and suppressed byaddition of NH₄ ⁺ ions (FIGS. 115( c) & (d)).

ee. Morphologies and Microstructures

FIG. 116 and FIG. 117 show the SEM of deposit surface obtained frombaths at temperature of 25 (at 25 mA/cm²) and 60° C. (at 300 mA/cm²),respectively. The morphology of deposits shows little effect of thesupporting electrolyte.

ff. Magnetic Properties

FIG. 118 shows the magnetic properties of deposits obtained fromsolutions with/without supporting electrolytes.

Addition of NH₄ sulfamate, NH₄Cl or KCl did not degrade deposit magneticsaturation (Ms). These Ms values were close to sputtered deposits (FIGS.118( a) & (b)). While Hc⊥ decreased sharply and Hc_(∥) varied littlewith increased Sm content, the addition of various supportingelectrolytes had little effect on deposit coercivity (FIGS. 118( c) &(d)). Both in-plane and perpendicular squareness (Mr/Ms) decreased withthe former significantly higher than the latter. Addition of supportingelectrolyte containing Cl—, especially KCl, resulted in higher in-planesquareness compared to deposits from other solutions at D60° C. (FIG.118(1)).

6. Aqueous Electrodeposition of Magentic Co—Sm Alloys—Pulse Current (PC)Electrodeposition Studies

In pulse current (PC) electrodeposition studies, an interrupted cathodiccurrent with square waveform is applied for a specific time period(T_(on)) and then returned to ground zero for another specific timeperiod (T_(off)); such a pulse period consisting of T_(on) and T_(off)repeats during the electrodeposition. Three important features in PCelectrodeposition are: peak current density (PCD), concentrationrelaxation of reactants and kinetic selected deposition [Ibl, J. C.Puippe and H. Angerer, Surf Tech., 6, 287, (1978); N. Ibl, Surf Tech.,10, 81, (1980).]. These characteristics of PC electrodeposition affectalloy compositions and crystal properties of deposits.

Pulse current results in a very high instantaneous peak current densityand hence a very negative cathodic potential. Higher CDs or morenegative cathodic potentials have been shown to increase Sm depositcontent in DC electrodeposition studies. Hull cell studies also showthis trend in PC electrodeposition. Therefore, PC electrodeposition ofhigh peak current densities can increase Sm deposit content. Inaddition, a very negative cathodic potential also increases thenucleation rate and can change the particle size and microstructures ofdeposits.

Short T_(on) and longer T_(off) provides more relaxation of the reactant(metal ions or complexes) concentrations at the cathode surfacepreventing the depletion of reactants and minimizing mass transfereffects. This changes the alloy composition. OH— ions were generatedonly during T_(on) in PC electrodeposition (DC generates OH— ionscontinuously during electrodeposition.). This can prevent unwanted Smand Co hydroxides/oxides in deposits.

Frequency of pulse current also change alloy compositions. Unlike DCobtaining deposits steadily during electrodeposition, PC enables thekinetic selected deposition by increased frequency. In alloyelectrodeposition, higher frequency increases deposit content of metalwith higher reduction rates.

Disclosed herein is how PC electrodeposition parameters affected alloyproperties (i.e., composition, crystal and magnetic properties), andcorrelate deposit magnetic behavior to other alloy properties. Inaddition, deposits obtained by DC and PC electrodeposition are compared.

The main goals of PC electrodeposition include: Obtaining high Smdeposit content of Co—Sm alloys; Determining the dependence of thedeposit properties of Co—Sm alloys on PC electrodeposition parameters;Studying the relation between the deposit magnetic properties and PCelectrodeposition parameters; Comparing deposit properties obtained byDC and PC electrodeposition.

FIG. 120 shows the experimental flowchart of a PC experiment whichmainly includes four parts: pretreatment of cathode, PCelectrodeposition, post-treatment of specimen and characterization.Definitions, setup and design of PC electrodeposition, pretreatment andpost-treatment, and the characterization and analysis of the specimenswill be detailed in following sections.

a. Definitions and Parameters of PC Electrodeposition

PCD (peak current density) is the maximum CD in one complete pulsecycle. T_(on), is the time duration of the on-current in one completepulse cycle. T_(off) is the time duration of the off-current in onecomplete pulse cycle. Period is the total time duration in one completepulse cycle, period=T_(total)=T_(on)+T_(off). Frequency is defined asthe number of complete cycles per second,

$f = {\frac{1}{period} = {\frac{1}{T_{on} + T_{off}}.}}$

Duty cycle (y) is defined as the ratio of Ton to period,

$\gamma = {\frac{T_{on}}{T_{on} + T_{off}} = {T_{on} \cdot {f.}}}$

PCD_(max) is defined as the highest PCD to obtain metallic appearingdeposits.

b. Setup of PC Electrodeposition

FIG. 122 shows the setup of the PC electrodeposition system. A KraftDynatronixpower generator (model DRP 20-5-10) served as the power sourcefor PC electrodeposition. A coulometer was used to measure the chargepassed during electrodeposition. The deposits were obtained in a 250 mlbeaker filled with the plating bath of 240 ml. Brass panels (2×1.9 cm)served as cathodes and a platinum sheet (3×36 cm) was used as the anode;the distance between the cathode and the anode is 4 cm. A shieldingpanel with a 2×2 cm opening window, designed by the simulation result ofANSYS (a finite element analysis software), was placed between thecathode and anode to provide a uniform current density distribution oncathode to minimize the thickness variation of the deposit.

C. Design of Experiments

In this study, operating conditions for PC electrodeposition, such aspeak current density, solution temperature, duty cycle, frequency andT_(on) will be varied. Various peak current densities (100-1200 mA/cm²),bath temperatures (25-60° C.), duty cycle (0.001-0.3), frequency (10-2 kHz), and To_(n) (0.05-2 ms) were used to obtain deposits. Bath 1 (1Msamarium sulfamate, 0.05M cobalt sulfate, 0.15M glycine) was used todetermine the key variables in the PC co-electrodeposition of Co—Smalloys.

d. Pretreatment and Post-Treatment

Before electrodeposition, the brass panels were mechanically cleaned,soaked in alkaline 0.1M NaOH solution for 10 min., rinsed in deionizedwater, immersed in 10% HCl for 30 seconds and than rinsed with deionizedwater. Unless otherwise noted, the total charge passed was 50 coulombs;solutions were not agitated during electrodeposition.

After the deposition of Co—Sm alloys for 50 coulombs, the deposits wereremoved from plating solution, rinsed with deionized water, and driedwith nitrogen gas. Disk-shaped specimens of diameter of 6.4 mm (specimenarea=31.7 mm²) were die-punched out from deposits for analysis.

e. Characterization and Analysis

The samarium

$\frac{Sm}{{Sm} + {Co}}\left( {{at}\%} \right)$

and cobalt deposit content

$\frac{Co}{{Sm} + {Co}}\left( {{at}\%} \right)$

were determined by an energy dispersive x-ray spectroscopy (EDS) with aKevex detector in a Cambridge SEM; the mass of deposited cobalt wasmeasured by a Perkin Elmer flame atomic absorption spectroscopy (AA,mode 631); the crystal structure, orientation, phase identification andgrain size were determined by a PANalytical x-ray diffraction system(XRD, model X'Pert Pro); the surface morphology, microstructure andgrain size were observed by a JEOL scanning electron microscopy (SEM,model JSM-6700F); magnetic properties were determined by a ADE Tech.vibrating sample magnetometer (VSM, model 1660). Unless otherwise noted,the experimental data presented are restricted to deposits with ametallic appearance.

f. Effect of PCD and Solution Temperature

Alloy Composition: Bath 1 (1M Sm sulfamate, 0.05M Co sulfate, 0.15Mglycine) was used to study the effects of peak current density (PCD) andsolution temperature on alloy properties. Ton was maintained constant as0.1 ms and duty cycle y of 0.1. FIG. 123 compares the effect of PCD (orCD) and solution temperature on Sm deposit content and currentefficiency in PC and DC electrodeposition. Similar to DCelectrodeposition, increased PCD resulted in increased Sm depositcontent. At 25° C., the PCD_(max) of 1050 mA/cm² was much higher thanthe CD_(max) of 50 mA/cm² resulting in a higher maximum. Sm depositcontent by PC (20.3 at %) than by DC (14.5 at %). On the other hand, at60° C. although the PCD_(max) (2100 mA/cm²) was higher than CD_(max)(500 mA/cm²), maximum Sm content by PC (11.6 at %) was lower than by DC(32.1 at %) due to smaller

$\frac{{{Sm}}\mspace{14mu} {content}}{{{PCD}}\mspace{14mu} \left( {{or}\mspace{14mu} {CD}} \right)}$

of PC electrodeposition. PC electrodeposition at 60° C. resulted in alower maximum Sm content (11.6 at %) compared to 25° C. (20.3 at %). Onthe other hand, DC electrodeposition showed the opposite result ofhigher maximum Sm content at 60° C. (32.1 at %) than 25° C. (14.5 at %).This confirms the Hull cell studies. Increased PCD led to decreasedcurrent efficiency, and elevated solution temperatures resulted inhigher current efficiencies in PC electrodeposition.

At 60° C., PC reduced Sm deposition and enhanced Co deposition comparedto DC electrodeposition (FIG. 124) resulting in lower Sm contents in PCelectrodeposition.

g. Crystal Structures

Compared to DC electrodeposition, Sm(OH)₃ was not found in deposits byPC electrodeposition (FIG. 125). DC generates OH— ions continuouslyduring electrodeposition. On the other hand, OH— ions were generatedonly during T_(on) in PC electrodeposition. Therefore, PCelectrodeposition resulted in lower OH— ion concentration at the cathodesurface and minimizing the folination of Sm(OH)₃ at both 25 and 60° C.

Deposits obtained at 25° C. (FIG. 125, left) appeared non-crystallinefor PCD higher than 200 mA/cm². Unlike DC electrodeposition,non-crystalline deposits were not found in PC electrodeposition at 60°C. (FIG. 125, right). All deposits obtained at 60° C. were hcpcrystallites, even up to 2100 mA/cm². The changes in orientation withincreased PCD (or Sm content) were different than DC and not inagreement with Pangarov's prediction [N. A. Pangarov, J. Electroanal.Chem., 9, 70, (1965).]. (00.2), (10.1), (11.0) and (10.0) peaks of hcpCo were observed for deposits without following any role.

h. Morphology and Microstructures

FIG. 126 and FIG. 127 shows the SEM of deposits obtained at 25 and 60°C., respectively. At 25° C., increased PCD resulted in increased Smdeposit content and decreased particle size, similar to DC. Also,microstructures changed from fiber-shaped nano-rods to roundishparticles, and microcracks increased with increased PCD.

However, for deposits obtained at 60° C., particle size decreasedsignificantly by increased PCD from 100 to 300 mA/cm² (FIGS. 127( c) &(f)) but changed little from 300 to 2100 mA/cm² (FIGS. 127( f), (i) &(1)). Ridge-shaped microstructures were observed in the depositsobtained at 100 mA/cm² (60° C.).

i. Magnetic Properties

FIG. 128 shows the hysteresis loops of deposits obtained at various PCDsand solution temperatures. Similar to deposits by DC electrodeposition,magnetization was easier in the in-plane direction than theperpendicular direction indicating the easy-axis (EA) along the in-planedirection and the hard axis (HA) along the perpendicular direction.In-plane magnetization (M_(∥)) was higher than perpendicularmagnetization (M⊥). On the other hand, Hc⊥ was higher than Hc_(∥). Withincreased PCD deposits changed from anisotropic to isotropic magneticbehavior at both 25 and 60° C. Such a change was more significant fordeposits obtained at 60° C. Ms and He increased as solution temperatureincreased from 25 to 60° C.

Magnetic properties of deposits by DC and PC electrodeposition arecompared in FIG. 129. (Magnetization was more complete in the in-planethan the perpendicular direction so that Msii is used to represent Ms inthe following discussion.) The strong dependence of magnetic propertiesof deposits on Sm content was similar to DC electrodeposition. PC Msdecreased linearly with increased Sm deposit content, in agreement withsputtered films [H. S. Cho, J. R. Salem, A. J. Kellock and R. B. Beyers,IEEE Trans. Magnetics, 33, 2890, (1997).] (FIGS. 129( a) & (d)).Increased Sm content caused decreased H⊥ but Hc_(∥) varied little (FIGS.129 (b) & (e)). Hc⊥ declined and approached Hc_(∥) with increased Smcontent. S_(∥) was higher than S⊥ confirming the aligning of the easyaxis of magnetization along the in-plane direction (FIGS. 129( c) &(f)). Without wishing to be bound by theory, it is beleieved thatdecreased S_(∥) and S⊥ with increased Sm content was due to theincreased non-crystallinity of deposits.

j. Effect of Duty Cycle

Alloy Composition: Bath 1 was used to study the effects of duty cycle onalloys properties with Ton=0.1 ms, PCD=200 or 500 mA/cm². An increase induty cycle (y) increased Sm content linearly at 25° C. and parabolicallyat 60° C. (FIG. 130( a)). Increased Sm content was more significant atthe lower solution temperature (25° C.) and higher PCD (500 mA/cm²). Onthe other hand, increased y resulted in exponentially decreasing currentefficiencies. The decrease was more significant for deposit obtained at25° C. than at 60° C.

Increased y did not enhance the deposition of Sm but considerablysuppressed the deposition of Co (FIG. 131) leading to increased Smdeposit content (FIG. 130( a)). It was concluded from the RDEexperimental results that mass transfer effects were greater for Co thanSm co-deposition. Increased y (decreased T_(off)) caused a lower Coconcentration at the cathode surface because less Co ions recovered frombulk solution for shorter T_(off), resulting in the decrease of Codeposition.

k. Crystal Structures, Morphologies and Microstructures

Increased γ resulted in increased Sm content and changed deposits fromcrystalline to non-crystalline structures at both 25 and 60° C. (FIG.132). Increased γ also induced more microcracks in deposits at both 25°C. (FIGS. 133( a) & (d)) and 60° C. (FIGS. 133( g), (j) & (m)) and ledto decreased particle size at 25° C. (FIGS. 133( c) & (f)) and 60° C.(FIGS. 133( i), (1) & (o)).

These deposit characteristics caused by increased Sm content were alsoobserved for DC electrodeposition. Increased Sm content in the Co—Smalloys could distort Co lattices probably changing the deposits fromcrystalline to non-crystalline structures and leading to moremicrocracks.

1. Magnetic Properties

FIG. 134 shows the magnetic properties of deposits obtained at variousγ. Similar to the previous observation (effect of PCD and solutiontemperature on magnetic properties), magnetic properties of depositsobtained at various γ can be correlated to their Sm content whichcontrolled the crystal structure and particle size. Ms values decreasedwith increased Sm content. Ms obtained from various γ (0.025-0.3) atboth 25 and 60° C. were in agreement with sputtered films [H. S. Cho, J.R. Salem, A. J. Kellock and R. B. Beyers, IEEE Trans. Magnetics, 33,2890, (1997).]. Hc⊥ was higher than Hc_(∥). Increased Sm contentdecreased Hc⊥ but Hc_(∥) varied little (FIGS. 134( b) & (e)). Hc⊥obtained at 25° C. decreased linearly with increasing Sm content, but at60° C. Hc⊥ decreased gradually for Sm content less than 10 at % thendropped sharply. S_(∥) was higher than S_(∥) Both S⊥ and S⊥ decreasedwith increased Sm content (FIGS. 134( c) & (f)).

m. Effect of Frequency

Alloy Composition: Bath 1 was used to study the effect of frequency.Duty cycle γ was kept constant at 0.1, solution temperature at 25° C.and PCD at 100, 250 and 500 mA/cm². Increased frequency resulted inlinear decrease in Sm deposit content (FIG. 135( a)).

Increased frequency enhanced Co deposition, especially at low PCD, butSm deposition varied little (FIG. 136) resulting in decreased Sm depositcontent. These results indicate that Co deposition rate was greater thanSm deposition rate during electrodeposition of Co—Sm alloys leading todecreased Sm content at higher frequencies. Generally, increasedfrequency resulted in increased current efficiency, except for thedeposits obtained at 100 mA/cm² and 2000 Hz.

n. Crystal Structures and Morphologies

With increased frequency, deposits obtained at 100 Am/cm² and 25° C.changed from non-crystalline to crystalline (FIG. 137 left) probably dueto decreased Sm content. At low frequencies (100 Hz, 7.1 at % Sm),characteristic peaks for crystallites were not found indicatingnon-crystalline deposits. At medium frequencies (200-1 k Hz, 6.1-4.7 at% Sm), crystallites of mixed (10.0) and (11.0) peaks were observed. Athigh frequencies (2 kHz, 1.7 at % Sm), there was a strong (00.2) peak.Deposits obtained at 25° C. and frequencies between 100 and 1 kHz hadsimilar morphologies (FIG. 137 right). Microcracks were present in thesedeposits. However, for the deposits obtained at 100 mA/cm² and highfrequency of 2 kHz, about 30% of the surface of the brass substrate wasnot covered by CoSm deposits (FIG. 137( d) right, FIGS. 138( a) & (b)).Increased PCD to 500 mA/cm², the brass substrate was fully covered bydeposits (FIGS. 138( c) & (d)). In other words, low coverage of depositsoccurred only at high frequencies (2 kHz) and low PCD (100 mA/cm²).

o. Magnetic Properties

FIG. 139 shows the effect of frequency on magnetic properties in PCelectrodeposition (25° C., γ=0.1). Similar to previous observations,magnetic properties of deposits were dependent on the SM content.

Ms values decreased linearly with increased Sm content and are inagreement with sputtered films [H. S. Cho, J.R. Salem, A. J. Kellock andR. B. Beyers, IEEE Trans. Magnetics, 33, 2890, (1997).] (FIG. 139( b))in the frequency range between 100 and 2,000 Hz. Increased Sm contentdecreased Hc⊥ but Hc_(∥) varied little (FIG. 139( c)). Although bothS_(∥) and S⊥ decreased with increased Sm content (FIG. 134 (d)), thedecrease was less significant compared to the effect of PCD and solutiontemperature (FIG. 129) and duty cycle (FIG. 134).

p. Effect of T_(on)

Alloy Composition: Bath 1 was used to study the effects of T_(on).Compared to studies discussed earlier, short T_(on) (0.1-2 ms) and longT_(off) (98-99.9 ms) were investigated to maintain the solutioncomposition at cathode surface close to the bulk composition uponinitiation of each pulse. By doing this, not only the effect of T_(on)but also the deposition rates of Sm and Co can be investigated. Pulseperiod (T_(on)+T_(off)) was fixed at 100 ms, solution temperature at 25°C. and PCD between 100 and 500 mA/cm².

Increased T_(on) resulted in a parabolic increase in Sm content (FIG.140( a)) at both 500 and 1000 mA/cm². Metallic deposits were obtained atT_(on) below 2 and 1 ms for 500 and 1000 mA/cm², respectively. HigherPCD reduced the maximum T_(on) for metallic deposits. The effects ofT_(on) on individual Sm and Co deposition were quite different.Increased T_(on) led to a slightly higher Sm deposition rate (FIG. 141).On the other hand, Co deposition increased, reached a maximum anddecreased with increased T_(on). After reaching a maximum, the decreasein Co deposition with increased T_(on) confirmed the mass transfereffects observed in the rotating disk electrode results. CE increased,reached a maximum and decreased with increased T_(on) (FIG. 140( b)).

q. Crystal Structure and Microstructures

FIG. 142 show the XRD (left) and the SEM (right) results of depositsobtained at 25° C. and 1000 mA/cm² with various T_(on). The (11.0) peakof Sm(OH)₃ was found in the deposit obtained at T_(on), of 0.1 ms (FIG.142( d)). With further increased T_(on), Sm(OH)₃ peaks disappeared. Atshort T_(on) of 0.1 ms, (00.2), (10.0) and (11.0) peaks of hcp-Coappeared in the deposit. When T_(on) increased to 1 ms, only the (10.0)peak was found. The change of deposit orientations with increased T_(on)is similar to DC electrodeposition at 60° C. Both of these changes weredue to increased Sm deposit content. Increased T_(on) resulted inincreased Sm content also leading to significant decrease inmicrostructure size (FIG. 142, right). Again, the dependence of crystalorientation and particle size on Sm content was observed.

r. Magnetic Properties

The effects of T_(on) on magnetic properties are shown in FIG. 143. Asdiscussed in previous sections: Ms values depended on alloy compositionand decreased linearly with increased Sm content in agreement withsputtered films. Hc⊥ was higher than Hc∥ and decreased with increasingSm content (FIG. 143( c)). S_(∥) were larger than S⊥ and both decreasedwith increased Sm content (FIG. 143( d)).

s. Deposition Rates of Sm and Co

In the previous section, long periods (100 ms), short T_(on) (0.1-2 ms)and low duty cycles (0.001-0.02) examined the effect of T_(on) on Smdeposit content. Because short T_(on) consumed less metal ions in asingle pulse and low duty cycle provided greater relaxation time for therecovery of metal ion concentrations, the metal ion concentration at thecathode surface probably remain close to the bulk solution concentrationjust before the beginning of each pulse. Therefore, we assumed that atthe initiation of each pulse the solution composition at the cathodeequaled the bulk solution. Thus, the deposit contents at each pulse wereidentical, and Sm and Co in deposits were assumed the result of thereduction of Sm and Co ions to metals rather than to precipitation ofSm(OH)₃ and Co(OH)₂. This provided a first approximation in thecalculation of the electrodeposition rates of Sm and Co.

The deposit content for each pulse was assumed to be identical.Therefore, the amount of electrodeposited Sm and Co per pulse atdifferent T_(on) can be calculated, as shown in Table 26.Electrodeposition rates at different time can be obtained by taking thedifference in deposit content (amount of Co and Sm) for pulses anddivided by the difference in time duration.

TABLE 26 Calculation of reaction rates of Sm and Co Pulse InformationDeposits for 50 C Deposits per Pulse Reaction Rate Ton charge per pulseSm Co Sm Co Time Sm Co (ms) pulse (C) number (mole) (mole) (mole) (mole)(ms) (mole)/s (mole)/s 0.1 1.90E−04 263158 2.3E−08 2.8E−06 8.7E−141.1E−11 0.05 8.7E−10 1.1E−07 0.3 5.70E−04 87719 1.4E−07 5.0E−06 1.6E−125.7E−11 0.20 7.5E−09 2.3E−07 0.5 9.50E−04 52632 2.9E−07 7.6E−06 5.6E−121.4E−10 0.40 2.0E−08 4.4E−07 0.7 1.33E−03 37594 3.2E−07 7.1E−06 8.4E−121.9E−10 0.60 1.4E−08 2.2E−07 1.0 1.90E−03 26316 3.4E−07 6.7E−06 1.3E−112.5E−10 0.85 1.5E−08 2.2E−07 1.3 2.47E−03 20243 3.9E−07 6.6E−06 1.9E−113.3E−10 1.15 2.1E−08 2.4E−07 1.6 3.04E−03 16447 4.2E−07 6.3E−06 2.5E−113.8E−10 1.45 2.1E−08 1.9E−07 2 3.80E−03 13158 4.5E−07 6.0E−06 3.4E−114.5E−10 1.80 2.1E−08 1.8E−07 charge per pulse (C) = PCD × area × T_(on)= 0.5(A/cm²) × 3.8 (cm²) × 0.0001 (sec) = 1.90E−04 pulse number = totalapplied charge/charge per pulse = 50/1.90E−04 = 263158 Deposits for 50 C(total applied charge): Sm: 2.3E−08 (mole) and Co: 2.8E−06 (mole) fromAA and EDS Deposits per Pulse: Deposits for 50 C/pulse number, Sm =2.3E−08/263158 = 8.7E−14 (mole) Co = 2.8E−06/263158 = 1.1E−11 (mole)Reaction Rate (at 0.05 ms): Deposits per Pulse/Deposit duration, Sm =8.7E−14/0.0001 = 8.7E−10 (mole/s) Co = 1.1E−11/0.0001 = 1.1E−07 (mole/s)Reaction Rate (at 0.2 ms = (0.1 ms + 0.3 ms)/2); Sm =(1.6E−12-8.7E−14)/(0.0003-0.0001) = 7.5E−09 (mole/s) Co =(5.7E−11-1.1E−11)/(0.0003-0.0001) = 2.3E−07 (mole/s)

The deposition rates of Sm and Co at various deposition times areplotted in FIG. 144. Deposition rates of Sm increased linearly withdeposition time. On the other hand, the deposition rate of Co increased,reached a maximum, and then decreased with increased deposition time.Higher PCD of 1000 mA/cm² resulted in higher deposition rates of both Smand Co compared to the lower PCD of 500 mA/cm². Higher PCD caused Codeposition rates to reach a maximum in a shorter deposition time (0.3 msfor 1000 mA/cm² and 0.4 ms for 500 mA/cm²). Co deposition rates weremuch higher than Sm deposition rates (about 10-120 times higherdepending on PCD and deposition time) indicating that Co deposition isfaster than Sm in agreement with results on frequency effects. Thedecrease in Co deposition rates after the maximum indicates masstransfer effects in the electrodeposition of Co—Sm alloys consistentwith the results of rotating disk electrode studies and the effect ofT_(on).

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the scope or spirit of the invention. Otheraspects of the invention will be apparent to those skilled in the artfrom consideration of the specification and practice of the inventiondisclosed herein. It is intended that the specification and examples beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims.

1. A composition for enhancing the aqueous electrodeposition of rareearth-transition metal alloys comprising: a water soluble salt ofsamarium, a water soluble salt of cobalt, and a complexant.
 2. Thecomposition of claim 1, wherein the water soluble salt of samarium issamarium sulfamate.
 3. The composition of claim 1, wherein the watersoluble salt of cobalt is cobalt sulfate or cobalt sulfamate.
 4. Thecomposition of claim 1, wherein the complexant is selected from one ormore amine carboxylates, one or more hydroxycarboxylic acids, andcombinations thereof.
 5. The composition of claim 1, further comprisingone or more supporting electrolytes.
 6. The composition of claim 5,wherein the one or more supporting electrolytes is selected fromammonium sulfamate, ammounium sulfate, ammonium chloride, and mixturesthereof.
 7. The composition of claim 1, comprising from about 0.25M toabout 2.0M of the water soluble salt of samarium, from about 0.01M toabout 0.5M of the water soluble salt of cobalt, from about 0.05M toabout 0.5M of the complexant, and from about 0M to about 3M of one ormore supporting electrolytes.
 8. The composition of claim 7, comprisingabout 1M of the water soluble salt of samarium, about 0.05M of the watersoluble salt of cobalt, about 0.15M of the complexant, and about 1M ofthe one or more supporting electrolytes.
 9. A method forelectrodepositing a samarium-cobalt coating onto a conducting substrate,comprising: a. placing an aqueous solution containing a water solublesalt of samarium, a water soluble salt of cobalt, one or more supportingelectrolytes, and a complexant into a plating bath, b. placing an anodeand the substrate to be coated into the bath and connecting the anodeand the substrate to a power supply, with the substrate acting as acathode, c. adjusting the pH of the bath to a suitable operating level,and d. applying a current through the anode and substrate causing thesamarium and the cobalt to migrate to, and adhere to, the substrate. 10.The method of claim 9, wherein the water soluble salt of samarium issamarium sulfamate.
 11. The method of claim 9, wherein the water solublesalt of cobalt is cobalt sulfate or cobalt sulfamate.
 12. The method ofclaim 9, wherein the complexant is selected from one or more aminecarboxylates, one or more hydroxycarboxylic acids, and combinationsthereof.
 13. The method of claim 9, wherein the one or more supportingelectrolytes is selected from ammonium sulfamate, ammounium sulfate,ammonium chloride, and mixtures thereof.
 14. The method of claim 9,wherein the aqueous solution further comprises boric acid.
 15. Themethod of claim 9, wherein the aqueous solution comprises from about0.25M to about 2.0M of the water soluble salt of samarium, from about0.01M to about 0.5M of the water soluble salt of cobalt, from about0.05M to about 0.5M of the complexant, and from about 0.0001M to about3M of the supporting electrolytes.
 16. The method of claim 15, whereinthe aqueous solution comprises about 1M of the water soluble salt ofsamarium, about 0.05M of the water soluble salt of cobalt, about 0.15Mof the complexant, and about 1M of the supporting electrolytes.
 17. Themethod of claim 9, wherein a current density of from about 5 mA/cm² toabout 600 mA/cm² is applied across the anode and cathode.
 18. The methodof claim 9, wherein the current is applied with pulse currentmodifications varying with duty cycle and frequency.
 19. The method ofclaim 9, wherein the pH of the solution is from about 4 to about 6.5.20. The method of claim 9, wherein the solution temperature is adjustedto from about 25° C. to about 60° C.
 21. A samarium-cobalt coatingproduced by the method of claim
 9. 22. A nanostructured magnetic coatingcomprising a magnetic alloy of a rare earth metal and a transitionmetal.
 23. The nanostructured magnetic coating of claim 22, wherein therare earth metal is samarium and wherein the transition metal is cobalt.24. The nanostructured magnetic coating of claim 22, wherein the coatingis provided by electrodeposition from an aqueous solution.
 25. Thenanostructured magnetic coating of claim 22, wherein the alloy comprisesSmCo₅ or Sm₂Co₁₇.